/* ============================================================
   LABVERSE — MASTER STYLESHEET v1.0
   ONE file. Every component. No duplicates.
   DO NOT edit individual sections in isolation.
   ============================================================ */

/* ============================================================
   1. CSS VARIABLES — DESIGN TOKENS
   ============================================================ */
:root {
  /* Colours */
  --color-primary:       #2563EB;
  --color-primary-light: #EFF6FF;
  --color-primary-mid:   #BFDBFE;
  --color-primary-dark:  #1D4ED8;
  --color-accent:        #3B82F6;
  --color-bg:            #F8FAFF;
  --color-surface:       #FFFFFF;
  --color-border:        #E8F0FE;
  --color-border-mid:    #CBD5E1;
  --color-text-primary:  #0F172A;
  --color-text-body:     #334155;
  --color-text-muted:    #64748B;
  --color-text-light:    #94A3B8;
  --color-success:       #10B981;
  --color-success-light: #ECFDF5;
  --color-warning:       #F59E0B;
  --color-warning-light: #FFFBEB;
  --color-danger:        #EF4444;
  --color-danger-light:  #FEF2F2;
  --color-info:          #06B6D4;
  --color-info-light:    #ECFEFF;
  --color-tip-light:     #F5F3FF;

  /* Footer intentionally stays dark navy in both themes for brand
     consistency — must NOT be tied to --color-text-primary, which
     flips to near-white in dark mode. */
  --color-footer-bg:     #0F172A;

  /* Typography */
  --font: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --text-xs:   0.75rem;
  --text-sm:   0.875rem;
  --text-base: 1rem;
  --text-lg:   1.125rem;
  --text-xl:   1.25rem;
  --text-2xl:  1.5rem;
  --text-3xl:  1.875rem;
  --text-4xl:  2.25rem;
  --text-5xl:  3rem;

  /* Spacing */
  --s1:0.25rem; --s2:0.5rem;  --s3:0.75rem; --s4:1rem;
  --s5:1.25rem; --s6:1.5rem;  --s8:2rem;    --s10:2.5rem;
  --s12:3rem;   --s16:4rem;   --s20:5rem;   --s24:6rem;

  /* Radius */
  --r-sm:0.375rem; --r-md:0.75rem; --r-lg:1rem;
  --r-xl:1.5rem;   --r-2xl:2rem;   --r-full:9999px;

  /* Shadows */
  --shadow-sm: 0 2px 8px rgba(37,99,235,0.06), 0 1px 3px rgba(0,0,0,0.05);
  --shadow-md: 0 4px 16px rgba(37,99,235,0.08), 0 2px 6px rgba(0,0,0,0.06);
  --shadow-lg: 0 8px 32px rgba(37,99,235,0.10), 0 4px 12px rgba(0,0,0,0.08);
  --shadow-xl: 0 16px 48px rgba(37,99,235,0.12), 0 8px 24px rgba(0,0,0,0.10);

  /* Transitions */
  --t-fast:150ms ease; --t-base:250ms ease; --t-slow:400ms ease;

  /* Layout */
  --nav-h:68px; --sidebar-w:280px; --content-max:860px; --page-max:1280px;
}

/* ============================================================
   2. DARK MODE
   ============================================================ */
[data-theme="dark"] {
  --color-bg:            #0B1120;
  --color-surface:       #111827;
  --color-border:        #1E293B;
  --color-border-mid:    #334155;
  --color-text-primary:  #F1F5F9;
  --color-text-body:     #CBD5E1;
  --color-text-muted:    #94A3B8;
  --color-text-light:    #64748B;
  --color-primary-light: #1E3A5F;
  --color-primary-mid:   #1D3A6E;
  --shadow-sm: 0 2px 8px rgba(0,0,0,0.30);
  --shadow-md: 0 4px 16px rgba(0,0,0,0.40);
  --shadow-lg: 0 8px 32px rgba(0,0,0,0.50);

  /* Tinted-card surfaces: dark, desaturated washes instead of the
     light-mode pastels — this is what keeps callouts from glaring
     against a near-black page. */
  --color-success-light: rgba(16,185,129,0.13);
  --color-warning-light: rgba(245,158,11,0.14);
  --color-danger-light:  rgba(239,68,68,0.13);
  --color-info-light:    rgba(6,182,212,0.13);
  --color-tip-light:     rgba(139,92,246,0.14);
}

/* ============================================================
   3. RESET & BASE
   ============================================================ */
@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700;800&display=swap');

*,*::before,*::after{box-sizing:border-box;margin:0;padding:0}
html{scroll-behavior:smooth;font-size:16px;-webkit-text-size-adjust:100%}
body{font-family:var(--font);font-size:var(--text-base);line-height:1.625;color:var(--color-text-body);background:var(--color-bg);transition:background var(--t-base),color var(--t-base);-webkit-font-smoothing:antialiased}
img{max-width:100%;height:auto;display:block}
a{color:var(--color-primary);text-decoration:none}
a:hover{text-decoration:underline}
ul,ol{list-style:none}
button{cursor:pointer;border:none;background:none;font-family:inherit}
input,textarea,select{font-family:inherit}
table{border-collapse:collapse;width:100%}

/* ============================================================
   4. TYPOGRAPHY
   ============================================================ */
h1,h2,h3,h4,h5,h6{font-family:var(--font);font-weight:700;color:var(--color-text-primary);line-height:1.25;letter-spacing:-0.02em}
h1{font-size:var(--text-4xl)} h2{font-size:var(--text-3xl)} h3{font-size:var(--text-2xl)}
h4{font-size:var(--text-xl)}  h5{font-size:var(--text-lg)}  h6{font-size:var(--text-base)}
p{margin-bottom:var(--s4);color:var(--color-text-body);line-height:1.625}
p:last-child{margin-bottom:0}
strong{font-weight:600;color:var(--color-text-primary)}
small{font-size:var(--text-sm);color:var(--color-text-muted)}

/* ============================================================
   5. LAYOUT
   ============================================================ */
.container{width:100%;max-width:var(--page-max);margin-inline:auto;padding-inline:var(--s6)}
.container-narrow{width:100%;max-width:var(--content-max);margin-inline:auto;padding-inline:var(--s6)}
.section{padding-block:var(--s20)}
.section-sm{padding-block:var(--s12)}

/* ============================================================
   6. NAVIGATION
   ============================================================ */
.nav{position:fixed;top:0;left:0;right:0;height:var(--nav-h);background:rgba(255,255,255,0.92);backdrop-filter:blur(16px);-webkit-backdrop-filter:blur(16px);border-bottom:1px solid var(--color-border);z-index:1000;transition:box-shadow var(--t-base),background var(--t-base)}
[data-theme="dark"] .nav{background:rgba(11,17,32,0.92)}
.nav.scrolled{box-shadow:var(--shadow-md)}
.nav-inner{display:flex;align-items:center;justify-content:space-between;height:100%;max-width:var(--page-max);margin-inline:auto;padding-inline:var(--s6)}

/* Logo */
.nav-logo{display:flex;align-items:center;gap:var(--s2);font-size:var(--text-xl);font-weight:800;color:var(--color-primary);letter-spacing:-0.03em;text-decoration:none}
.nav-logo:hover{text-decoration:none}
.nav-logo-mark{width:36px;height:36px;background:var(--color-primary);border-radius:var(--r-sm);display:flex;align-items:center;justify-content:center;color:white;font-size:var(--text-sm);font-weight:800;flex-shrink:0}
.nav-logo-text{color:var(--color-text-primary)}
.nav-logo-text span{color:var(--color-primary)}

/* Links */
.nav-links{display:flex;align-items:center;gap:var(--s1)}
.nav-link{font-size:var(--text-sm);font-weight:500;color:var(--color-text-muted);padding:var(--s2) var(--s3);border-radius:var(--r-sm);transition:all var(--t-fast);text-decoration:none}
.nav-link:hover,.nav-link.active{color:var(--color-primary);background:var(--color-primary-light);text-decoration:none}

/* Actions */
.nav-actions{display:flex;align-items:center;gap:var(--s3)}
.nav-search-btn{display:flex;align-items:center;gap:var(--s2);padding:var(--s2) var(--s4);background:var(--color-bg);border:1px solid var(--color-border);border-radius:var(--r-full);font-size:var(--text-sm);color:var(--color-text-muted);cursor:pointer;transition:all var(--t-fast)}
.nav-search-btn:hover{border-color:var(--color-primary-mid);color:var(--color-primary)}
.theme-toggle{width:36px;height:36px;border-radius:var(--r-full);background:var(--color-bg);border:1px solid var(--color-border);display:flex;align-items:center;justify-content:center;cursor:pointer;transition:all var(--t-fast);font-size:var(--text-base);color:var(--color-text-muted)}
.theme-toggle:hover{background:var(--color-primary-light);border-color:var(--color-primary-mid);color:var(--color-primary)}

/* Mobile */
.nav-mobile-btn{display:none;width:36px;height:36px;border-radius:var(--r-sm);background:var(--color-bg);border:1px solid var(--color-border);align-items:center;justify-content:center;cursor:pointer;flex-direction:column;gap:4px;padding:8px}
.nav-mobile-btn span{display:block;width:18px;height:2px;background:var(--color-text-primary);border-radius:2px;transition:all var(--t-base)}
.nav-mobile-btn.open span:nth-child(1){transform:translateY(6px) rotate(45deg)}
.nav-mobile-btn.open span:nth-child(2){opacity:0}
.nav-mobile-btn.open span:nth-child(3){transform:translateY(-6px) rotate(-45deg)}
.nav-mobile-menu{display:none;position:fixed;top:var(--nav-h);left:0;right:0;bottom:0;background:var(--color-surface);z-index:999;padding:var(--s6);flex-direction:column;gap:var(--s2);overflow-y:auto}
.nav-mobile-menu.open{display:flex;animation:slideDown var(--t-base) ease}
.nav-mobile-link{display:flex;align-items:center;padding:var(--s4);border-radius:var(--r-md);font-size:var(--text-lg);font-weight:500;color:var(--color-text-primary);text-decoration:none;transition:background var(--t-fast)}
.nav-mobile-link:hover{background:var(--color-primary-light);color:var(--color-primary);text-decoration:none}
.page-body{padding-top:var(--nav-h)}

/* ============================================================
   7. BREADCRUMB
   ============================================================ */
.breadcrumb{display:flex;align-items:center;gap:var(--s2);flex-wrap:wrap;padding:var(--s4) 0;font-size:var(--text-sm)}
.breadcrumb-item{color:var(--color-text-muted);text-decoration:none;transition:color var(--t-fast)}
.breadcrumb-item:hover{color:var(--color-primary)}
.breadcrumb-sep{color:var(--color-text-light);font-size:var(--text-xs)}
.breadcrumb-current{color:var(--color-text-primary);font-weight:500}

/* ============================================================
   8. HEROES
   ============================================================ */

/* Home hero */
.hero{padding-block:var(--s24);background:linear-gradient(135deg,var(--color-primary-light) 0%,#fff 60%);position:relative;overflow:hidden;text-align:center}
[data-theme="dark"] .hero{background:linear-gradient(135deg,#0d1f3c 0%,var(--color-bg) 60%)}
.hero::before{content:'';position:absolute;top:-50%;right:-20%;width:700px;height:700px;background:radial-gradient(circle,rgba(37,99,235,0.07) 0%,transparent 70%);pointer-events:none}
.hero-eyebrow{display:inline-flex;align-items:center;gap:var(--s2);background:var(--color-primary-light);border:1px solid var(--color-primary-mid);color:var(--color-primary);font-size:var(--text-sm);font-weight:600;padding:var(--s2) var(--s4);border-radius:var(--r-full);margin-bottom:var(--s6);letter-spacing:0.02em}
.hero-title{font-size:clamp(2rem,5vw,3.75rem);font-weight:800;letter-spacing:-0.03em;color:var(--color-text-primary);line-height:1.1;margin-bottom:var(--s6)}
.hero-title .hl{color:var(--color-primary)}
.hero-subtitle{font-size:var(--text-lg);color:var(--color-text-muted);max-width:580px;margin-inline:auto;margin-bottom:var(--s10);line-height:1.625}
.hero-actions{display:flex;gap:var(--s4);justify-content:center;flex-wrap:wrap}
.hero-stats{display:flex;justify-content:center;gap:var(--s12);margin-top:var(--s16);flex-wrap:wrap}
.hero-stat-n{font-size:var(--text-3xl);font-weight:800;color:var(--color-primary);letter-spacing:-0.03em;display:block}
.hero-stat-l{font-size:var(--text-sm);color:var(--color-text-muted);margin-top:var(--s1)}

/* Lesson hero */
.lesson-hero{background:linear-gradient(135deg,#1D4ED8 0%,#2563EB 100%);color:white;padding:var(--s12) 0 var(--s10);position:relative;overflow:hidden}
.lesson-hero::before{content:'';position:absolute;inset:0;background:url("data:image/svg+xml,%3Csvg width='60' height='60' viewBox='0 0 60 60' xmlns='http://www.w3.org/2000/svg'%3E%3Cg fill='%23ffffff' fill-opacity='0.03'%3E%3Ccircle cx='30' cy='30' r='25'/%3E%3C/g%3E%3C/svg%3E");pointer-events:none}
.lesson-hero-inner{position:relative;z-index:1}
.lesson-subject-tag{display:inline-flex;align-items:center;gap:var(--s2);background:rgba(255,255,255,0.15);border:1px solid rgba(255,255,255,0.25);color:white;font-size:var(--text-sm);font-weight:600;padding:var(--s1) var(--s3);border-radius:var(--r-full);margin-bottom:var(--s3);backdrop-filter:blur(8px)}
.lesson-no{font-size:var(--text-sm);font-weight:600;color:rgba(255,255,255,0.70);margin-bottom:var(--s2);letter-spacing:0.06em;text-transform:uppercase}
.lesson-hero h1{color:white;font-size:clamp(1.75rem,4vw,2.75rem);margin-bottom:var(--s5);max-width:820px}
.lesson-meta{display:flex;flex-wrap:wrap;gap:var(--s4);margin-bottom:var(--s5)}
.lesson-meta-item{display:flex;align-items:center;gap:var(--s2);font-size:var(--text-sm);color:rgba(255,255,255,0.80)}
.lesson-hero-btns{display:flex;align-items:center;gap:var(--s3);flex-wrap:wrap;margin-top:var(--s5)}

/* Badge */
.badge{display:inline-flex;align-items:center;gap:var(--s1);padding:var(--s1) var(--s3);border-radius:var(--r-full);font-size:var(--text-xs);font-weight:600;letter-spacing:0.04em;text-transform:uppercase}
.badge-easy  {background:var(--color-success-light);color:var(--color-success)}
.badge-medium{background:var(--color-warning-light); color:var(--color-warning)}
.badge-hard  {background:var(--color-danger-light);  color:var(--color-danger)}

/* ============================================================
   9. BUTTONS
   ============================================================ */
.btn{display:inline-flex;align-items:center;justify-content:center;gap:var(--s2);padding:var(--s3) var(--s6);border-radius:var(--r-md);font-size:var(--text-sm);font-weight:600;font-family:inherit;cursor:pointer;text-decoration:none;border:2px solid transparent;transition:all var(--t-base);white-space:nowrap;line-height:1;user-select:none}
.btn:hover{text-decoration:none;transform:translateY(-1px)}
.btn:active{transform:translateY(0)}
.btn-primary{background:var(--color-primary);color:white;border-color:var(--color-primary);box-shadow:0 4px 14px rgba(37,99,235,0.30)}
.btn-primary:hover{background:var(--color-primary-dark);border-color:var(--color-primary-dark);box-shadow:0 6px 20px rgba(37,99,235,0.40);color:white}
.btn-secondary{background:var(--color-surface);color:var(--color-primary);border-color:var(--color-primary-mid)}
.btn-secondary:hover{background:var(--color-primary-light);border-color:var(--color-primary);color:var(--color-primary)}
.btn-ghost{background:transparent;color:var(--color-text-body);border-color:var(--color-border)}
.btn-ghost:hover{background:var(--color-bg);border-color:var(--color-border-mid);color:var(--color-text-primary)}
.btn-white{background:white;color:var(--color-primary);border-color:white;box-shadow:var(--shadow-md)}
.btn-white:hover{background:var(--color-primary-light);color:var(--color-primary-dark)}
.btn-ghost-white{background:rgba(255,255,255,0.12);color:white;border-color:rgba(255,255,255,0.30)}
.btn-ghost-white:hover{background:rgba(255,255,255,0.22);border-color:rgba(255,255,255,0.50);color:white}
.btn-sm{padding:var(--s2) var(--s4);font-size:var(--text-xs);border-radius:var(--r-sm)}
.btn-lg{padding:var(--s4) var(--s8);font-size:var(--text-base);border-radius:var(--r-lg)}
.btn-icon{width:36px;height:36px;padding:0;border-radius:var(--r-sm);background:var(--color-bg);border:1px solid var(--color-border);color:var(--color-text-muted)}
.btn-icon:hover{background:var(--color-primary-light);border-color:var(--color-primary-mid);color:var(--color-primary);transform:none}

/* ============================================================
   10. CARDS
   ============================================================ */
.card{background:var(--color-surface);border-radius:var(--r-xl);border:1px solid var(--color-border);box-shadow:var(--shadow-sm);overflow:hidden;transition:box-shadow var(--t-base),transform var(--t-base)}
.card:hover{box-shadow:var(--shadow-lg);transform:translateY(-2px)}
.card-body{padding:var(--s6)}
.card-header{padding:var(--s5) var(--s6);border-bottom:1px solid var(--color-border)}
.card-footer{padding:var(--s4) var(--s6);border-top:1px solid var(--color-border);background:var(--color-bg)}

/* Subject card */
.subject-card{background:var(--color-surface);border-radius:var(--r-xl);border:1px solid var(--color-border);box-shadow:var(--shadow-sm);overflow:hidden;transition:all var(--t-base);text-decoration:none;display:block}
.subject-card:hover{box-shadow:var(--shadow-lg);transform:translateY(-3px);border-color:var(--color-primary-mid);text-decoration:none}
.subject-card-bar{height:6px;background:var(--color-primary)}
.subject-card-body{padding:var(--s6)}
.subject-card-icon{width:52px;height:52px;border-radius:var(--r-md);background:var(--color-primary-light);display:flex;align-items:center;justify-content:center;font-size:1.5rem;margin-bottom:var(--s4)}
.subject-card-title{font-size:var(--text-xl);font-weight:700;color:var(--color-text-primary);margin-bottom:var(--s2)}
.subject-card-desc{font-size:var(--text-sm);color:var(--color-text-muted);line-height:1.625;margin-bottom:var(--s4)}
.subject-card-meta{display:flex;align-items:center;justify-content:space-between;font-size:var(--text-xs);color:var(--color-text-muted)}

/* Lesson card */
.lesson-card{background:var(--color-surface);border-radius:var(--r-lg);border:1px solid var(--color-border);padding:var(--s5);display:flex;align-items:flex-start;gap:var(--s4);transition:all var(--t-base);text-decoration:none}
.lesson-card:hover{box-shadow:var(--shadow-md);border-color:var(--color-primary-mid);transform:translateY(-1px);text-decoration:none}
.lesson-card.completed  {border-left:4px solid var(--color-success)}
.lesson-card.in-progress{border-left:4px solid var(--color-primary)}
.lesson-card.locked     {opacity:.55;pointer-events:none}
.lesson-card-num{width:40px;height:40px;border-radius:var(--r-sm);background:var(--color-primary-light);color:var(--color-primary);font-weight:700;font-size:var(--text-sm);display:flex;align-items:center;justify-content:center;flex-shrink:0}
.lesson-card.completed .lesson-card-num{background:var(--color-success-light);color:var(--color-success)}
.lesson-card-info{flex:1;min-width:0}
.lesson-card-title{font-size:var(--text-base);font-weight:600;color:var(--color-text-primary);margin-bottom:var(--s2);line-height:1.375}
.lesson-card-meta{display:flex;align-items:center;gap:var(--s3);flex-wrap:wrap}
.lesson-card-action{display:flex;align-items:center;gap:var(--s2);flex-shrink:0}

/* ============================================================
   11. PROGRESS
   ============================================================ */
.reading-progress{position:fixed;top:var(--nav-h);left:0;right:0;height:3px;background:var(--color-border);z-index:999}
.reading-progress-fill{height:100%;background:linear-gradient(90deg,var(--color-primary),var(--color-accent));width:0%;transition:width 80ms linear;border-radius:0 var(--r-full) var(--r-full) 0}
.progress-bar{width:100%;height:6px;background:var(--color-border);border-radius:var(--r-full);overflow:hidden}
.progress-fill{height:100%;background:linear-gradient(90deg,var(--color-primary),var(--color-accent));border-radius:var(--r-full);transition:width var(--t-slow)}
.progress-fill.success{background:var(--color-success)}
.progress-labeled{display:flex;flex-direction:column;gap:var(--s2)}
.progress-label-row{display:flex;justify-content:space-between;font-size:var(--text-sm);color:var(--color-text-muted)}
.course-progress-widget{background:var(--color-primary-light);border:1px solid var(--color-primary-mid);border-radius:var(--r-lg);padding:var(--s4) var(--s5)}

/* ============================================================
   12. INFO CARDS
   ============================================================ */
.info-card{border-radius:var(--r-lg);padding:var(--s5);display:flex;gap:var(--s4);border:1px solid;margin-bottom:var(--s4)}
.info-icon{font-size:1.25rem;flex-shrink:0;margin-top:2px}
.info-body{flex:1;min-width:0}
.info-title{font-size:var(--text-sm);font-weight:600;margin-bottom:var(--s1);letter-spacing:0.02em}
.info-text{font-size:var(--text-sm);line-height:1.625;margin:0}
.info-card.info   {background:var(--color-info-light);   border-color:rgba(6,182,212,0.25)}
.info-card.info   .info-title{color:#0E7490}.info-card.info   .info-text{color:#164E63}
.info-card.warning{background:var(--color-warning-light);border-color:rgba(245,158,11,0.25)}
.info-card.warning .info-title{color:#92400E}.info-card.warning .info-text{color:#78350F}
.info-card.danger {background:var(--color-danger-light); border-color:rgba(239,68,68,0.25)}
.info-card.danger .info-title{color:#B91C1C}.info-card.danger .info-text{color:#991B1B}
.info-card.success{background:var(--color-success-light);border-color:rgba(16,185,129,0.25)}
.info-card.success .info-title{color:#065F46}.info-card.success .info-text{color:#064E3B}
.info-card.tip    {background:var(--color-tip-light,#F5F3FF);border-color:rgba(139,92,246,0.25)}
.info-card.tip    .info-title{color:#5B21B6}.info-card.tip    .info-text{color:#4C1D95}

/* ============================================================
   13. ACCORDION
   ============================================================ */
.accordion{border-radius:var(--r-xl);overflow:hidden;border:1px solid var(--color-border);box-shadow:var(--shadow-sm);margin-bottom:var(--s4)}
.accordion-item{border-bottom:1px solid var(--color-border)}
.accordion-item:last-child{border-bottom:none}
.accordion-trigger{width:100%;display:flex;align-items:center;justify-content:space-between;padding:var(--s5) var(--s6);background:var(--color-surface);cursor:pointer;text-align:left;transition:background var(--t-fast);gap:var(--s4);border:none;font-family:inherit}
.accordion-trigger:hover{background:var(--color-bg)}
.accordion-trigger.active{background:var(--color-primary-light)}
.acc-left{display:flex;align-items:center;gap:var(--s3);min-width:0}
.acc-icon{font-size:1.1rem;flex-shrink:0}
.acc-title{font-size:var(--text-base);font-weight:600;color:var(--color-text-primary)}
.accordion-trigger.active .acc-title{color:var(--color-primary)}
.acc-chevron{font-size:var(--text-sm);color:var(--color-text-muted);flex-shrink:0;transition:transform var(--t-base);display:inline-block}
.accordion-trigger.active .acc-chevron{transform:rotate(180deg)}
.accordion-content{max-height:0;overflow:hidden;transition:max-height var(--t-slow) ease}
.accordion-content.open{max-height:9999px}
.accordion-inner{padding:var(--s6)}

/* ============================================================
   14. TABS
   ============================================================ */
.tabs{margin-bottom:var(--s6)}
.tabs-nav{display:flex;gap:var(--s1);border-bottom:2px solid var(--color-border);margin-bottom:var(--s6);overflow-x:auto;scrollbar-width:none}
.tabs-nav::-webkit-scrollbar{display:none}
.tab-btn{padding:var(--s3) var(--s5);font-size:var(--text-sm);font-weight:500;color:var(--color-text-muted);border:none;background:none;cursor:pointer;border-bottom:2px solid transparent;margin-bottom:-2px;white-space:nowrap;transition:all var(--t-fast);font-family:inherit;border-radius:var(--r-sm) var(--r-sm) 0 0}
.tab-btn:hover{color:var(--color-primary)}
.tab-btn.active{color:var(--color-primary);border-bottom-color:var(--color-primary);font-weight:600}
.tab-panel{display:none}
.tab-panel.active{display:block;animation:fadeIn var(--t-base) ease}

/* ============================================================
   15. FLASHCARDS
   ============================================================ */
.flashcard-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(280px,1fr));gap:var(--s4)}
.flashcard{height:220px;perspective:1000px;cursor:pointer}
.flashcard-inner{width:100%;height:100%;position:relative;transform-style:preserve-3d;transition:transform .6s cubic-bezier(0.23,1,0.32,1)}
.flashcard.flipped .flashcard-inner{transform:rotateY(180deg)}
.flashcard-front,.flashcard-back{position:absolute;inset:0;border-radius:var(--r-xl);padding:var(--s6);display:flex;flex-direction:column;align-items:center;justify-content:center;text-align:center;backface-visibility:hidden;-webkit-backface-visibility:hidden;border:1px solid var(--color-border);box-shadow:var(--shadow-md)}
.flashcard-front{background:var(--color-surface)}
.flashcard-back{background:var(--color-primary);color:white;transform:rotateY(180deg)}
.fc-label{font-size:var(--text-xs);font-weight:600;letter-spacing:0.08em;text-transform:uppercase;color:var(--color-text-muted);margin-bottom:var(--s3)}
.flashcard-back .fc-label{color:rgba(255,255,255,0.65)}
.fc-term{font-size:var(--text-lg);font-weight:700;color:var(--color-text-primary);line-height:1.375}
.flashcard-back .fc-term{color:white;font-size:var(--text-base);font-weight:400;line-height:1.625}
.fc-hint{font-size:var(--text-xs);color:var(--color-text-light);margin-top:var(--s4);display:flex;align-items:center;gap:var(--s1)}
.flashcard-back .fc-hint{color:rgba(255,255,255,0.55)}
.flashcard-single{max-width:520px;margin:0 auto;height:300px}
.flashcard-controls{display:flex;justify-content:center;align-items:center;gap:var(--s4);margin-top:var(--s6)}
.flashcard-counter{font-size:var(--text-sm);color:var(--color-text-muted);min-width:60px;text-align:center}

/* ============================================================
   16. QUIZ
   ============================================================ */
.quiz-widget{background:var(--color-surface);border-radius:var(--r-xl);border:1px solid var(--color-border);box-shadow:var(--shadow-md);overflow:hidden}
.quiz-header{padding:var(--s5) var(--s6);background:var(--color-primary-light);border-bottom:1px solid var(--color-border);display:flex;align-items:center;justify-content:space-between;flex-wrap:wrap;gap:var(--s3)}
.quiz-header-title{font-size:var(--text-lg);font-weight:700;color:var(--color-text-primary)}
.quiz-header-meta{font-size:var(--text-sm);color:var(--color-text-muted);display:flex;gap:var(--s4)}
.quiz-body{padding:var(--s8) var(--s6)}
.quiz-q-type{font-size:var(--text-xs);font-weight:600;letter-spacing:0.06em;text-transform:uppercase;color:var(--color-primary);display:block;margin-bottom:var(--s2)}
.quiz-question{font-size:var(--text-lg);font-weight:600;color:var(--color-text-primary);margin-bottom:var(--s6);line-height:1.375}
.quiz-options{display:flex;flex-direction:column;gap:var(--s3);margin-bottom:var(--s6)}
.quiz-option{display:flex;align-items:flex-start;gap:var(--s3);padding:var(--s4) var(--s5);border-radius:var(--r-lg);border:2px solid var(--color-border);background:var(--color-surface);cursor:pointer;transition:all var(--t-fast);text-align:left;font-family:inherit;font-size:var(--text-base);color:var(--color-text-body);width:100%}
.quiz-option:hover   {border-color:var(--color-primary-mid);background:var(--color-primary-light);color:var(--color-primary)}
.quiz-option.selected{border-color:var(--color-primary);background:var(--color-primary-light)}
.quiz-option.correct {border-color:var(--color-success);background:var(--color-success-light);color:var(--color-success)}
.quiz-option.incorrect{border-color:var(--color-danger);background:var(--color-danger-light);color:var(--color-danger)}
.quiz-opt-letter{width:28px;height:28px;border-radius:var(--r-full);background:var(--color-bg);border:1px solid var(--color-border);display:flex;align-items:center;justify-content:center;font-size:var(--text-sm);font-weight:700;flex-shrink:0;color:var(--color-text-primary);transition:all var(--t-fast)}
.quiz-option.correct  .quiz-opt-letter{background:var(--color-success);border-color:var(--color-success);color:white}
.quiz-option.incorrect .quiz-opt-letter{background:var(--color-danger); border-color:var(--color-danger); color:white}
.quiz-option.selected  .quiz-opt-letter{background:var(--color-primary);border-color:var(--color-primary);color:white}
.quiz-feedback{border-radius:var(--r-md);padding:var(--s4) var(--s5);margin-bottom:var(--s5);font-size:var(--text-sm);display:none}
.quiz-feedback.show{display:block;animation:fadeIn var(--t-base)}
.quiz-feedback.correct  {background:var(--color-success-light);color:#065F46;border:1px solid rgba(16,185,129,0.3)}
.quiz-feedback.incorrect{background:var(--color-danger-light); color:#B91C1C;border:1px solid rgba(239,68,68,0.3)}
.quiz-footer{padding:var(--s5) var(--s6);border-top:1px solid var(--color-border);display:flex;align-items:center;justify-content:space-between;flex-wrap:wrap;gap:var(--s4)}
.quiz-score-screen{text-align:center;padding:var(--s12) var(--s6)}
.quiz-score-circle{width:130px;height:130px;border-radius:50%;border:6px solid var(--color-primary);display:flex;flex-direction:column;align-items:center;justify-content:center;margin:0 auto var(--s6)}
.quiz-score-n{font-size:var(--text-4xl);font-weight:800;color:var(--color-primary);line-height:1}
.quiz-score-l{font-size:var(--text-xs);color:var(--color-text-muted)}
.quiz-tf{display:grid;grid-template-columns:1fr 1fr;gap:var(--s4);margin-bottom:var(--s6)}
.quiz-fill{width:100%;padding:var(--s3) var(--s4);border:2px solid var(--color-border);border-radius:var(--r-md);font-size:var(--text-base);font-family:inherit;background:var(--color-surface);color:var(--color-text-primary);transition:border-color var(--t-fast);outline:none;margin-bottom:var(--s4)}
.quiz-fill:focus{border-color:var(--color-primary)}
.quiz-match{display:grid;grid-template-columns:1fr 1fr;gap:var(--s3);margin-bottom:var(--s6)}
.quiz-match-col-label{font-size:var(--text-xs);font-weight:700;text-transform:uppercase;letter-spacing:0.06em;color:var(--color-text-muted);margin-bottom:var(--s2);padding-left:var(--s3)}
.quiz-match-item{padding:var(--s3) var(--s4);border-radius:var(--r-md);border:1px solid var(--color-border);background:var(--color-surface);font-size:var(--text-sm);cursor:pointer;transition:all var(--t-fast);user-select:none}
.quiz-match-item:hover  {border-color:var(--color-primary-mid);background:var(--color-primary-light);color:var(--color-primary)}
.quiz-match-item.picked {border-color:var(--color-primary);background:var(--color-primary-light);color:var(--color-primary)}
.quiz-match-item.matched{border-color:var(--color-success);background:var(--color-success-light);color:var(--color-success)}

/* ============================================================
   17. CLINICAL CASE CARD
   ============================================================ */
.case-card{background:var(--color-surface);border-radius:var(--r-xl);border:1px solid var(--color-border);box-shadow:var(--shadow-md);overflow:hidden}
.case-card-header{background:linear-gradient(135deg,#1E3A5F,#2563EB);color:white;padding:var(--s5) var(--s6);display:flex;align-items:center;gap:var(--s4)}
.case-avatar{width:48px;height:48px;border-radius:50%;background:rgba(255,255,255,0.15);display:flex;align-items:center;justify-content:center;font-size:1.5rem;flex-shrink:0}
.case-patient-name{font-size:var(--text-lg);font-weight:700;color:white;margin-bottom:2px}
.case-patient-meta{font-size:var(--text-sm);color:rgba(255,255,255,0.75)}
.case-card-body{padding:var(--s6)}
.case-section{margin-bottom:var(--s5);padding-bottom:var(--s5);border-bottom:1px solid var(--color-border)}
.case-section:last-child{border-bottom:none;margin-bottom:0;padding-bottom:0}
.case-section-label{font-size:var(--text-xs);font-weight:700;letter-spacing:0.08em;text-transform:uppercase;color:var(--color-primary);margin-bottom:var(--s3);display:flex;align-items:center;gap:var(--s2)}
.case-result-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(160px,1fr));gap:var(--s3)}
.case-result-item{background:var(--color-bg);border-radius:var(--r-md);padding:var(--s3);border:1px solid var(--color-border)}
.case-result-name{font-size:var(--text-xs);color:var(--color-text-muted);margin-bottom:var(--s1)}
.case-result-value{font-size:var(--text-base);font-weight:700;color:var(--color-text-primary)}
.case-result-value.abnormal{color:var(--color-danger)}
.case-result-value.borderline{color:var(--color-warning)}
.case-dx-badge{display:inline-flex;align-items:center;gap:var(--s2);background:var(--color-primary-light);border:1px solid var(--color-primary-mid);color:var(--color-primary);font-size:var(--text-sm);font-weight:600;padding:var(--s2) var(--s4);border-radius:var(--r-full)}

/* ============================================================
   18. LAB TIP / WARNING / SUMMARY
   ============================================================ */
.lab-tip{background:var(--color-tip-light,#F5F3FF);border:1px solid rgba(139,92,246,0.2);border-left:4px solid #8B5CF6;border-radius:var(--r-lg);padding:var(--s5);margin-bottom:var(--s4)}
.lab-tip-hd{display:flex;align-items:center;gap:var(--s2);font-size:var(--text-sm);font-weight:700;color:#5B21B6;margin-bottom:var(--s2);text-transform:uppercase;letter-spacing:0.03em}
.lab-tip-body{font-size:var(--text-sm);color:#4C1D95;line-height:1.625;margin:0}

.warning-card{background:var(--color-danger-light);border:1px solid rgba(239,68,68,0.2);border-left:4px solid var(--color-danger);border-radius:var(--r-lg);padding:var(--s5);margin-bottom:var(--s4)}
.warning-card-hd{display:flex;align-items:center;gap:var(--s2);font-size:var(--text-sm);font-weight:700;color:#B91C1C;margin-bottom:var(--s2);text-transform:uppercase;letter-spacing:0.03em}
.warning-card-body{font-size:var(--text-sm);color:#991B1B;line-height:1.625;margin:0}

.summary-card{background:var(--color-success-light);border:1px solid rgba(16,185,129,0.2);border-left:4px solid var(--color-success);border-radius:var(--r-lg);padding:var(--s5);margin-bottom:var(--s4)}
.summary-card-hd{display:flex;align-items:center;gap:var(--s2);font-size:var(--text-sm);font-weight:700;color:#065F46;margin-bottom:var(--s3);text-transform:uppercase;letter-spacing:0.03em}
.summary-list{list-style:none;margin:0;padding:0;display:flex;flex-direction:column;gap:var(--s2)}
.summary-list li{display:flex;gap:var(--s2);font-size:var(--text-sm);color:#064E3B;line-height:1.625}
.summary-list li::before{content:'✓';color:var(--color-success);font-weight:700;flex-shrink:0}

/* ============================================================
   19. COMPETENCY CHECKLIST
   ============================================================ */
.competency{background:var(--color-surface);border-radius:var(--r-xl);border:2px solid var(--color-primary-mid);overflow:hidden;box-shadow:var(--shadow-md)}
.competency-hd{background:var(--color-primary-light);padding:var(--s5) var(--s6);border-bottom:1px solid var(--color-primary-mid);display:flex;align-items:center;justify-content:space-between}
.competency-hd-title{font-size:var(--text-base);font-weight:700;color:var(--color-primary);display:flex;align-items:center;gap:var(--s2)}
.competency-score{font-size:var(--text-sm);font-weight:600;color:var(--color-text-muted)}
.competency-body{padding:var(--s5) var(--s6)}
.competency-item{display:flex;align-items:flex-start;gap:var(--s3);padding:var(--s3) 0;border-bottom:1px solid var(--color-border);cursor:pointer;user-select:none}
.competency-item:last-child{border-bottom:none}
.competency-box{width:22px;height:22px;border:2px solid var(--color-border-mid);border-radius:var(--r-sm);display:flex;align-items:center;justify-content:center;flex-shrink:0;transition:all var(--t-fast);margin-top:1px}
.competency-item.checked .competency-box{background:var(--color-primary);border-color:var(--color-primary);color:white}
.competency-text{font-size:var(--text-sm);color:var(--color-text-body);line-height:1.375;transition:color var(--t-fast)}
.competency-item.checked .competency-text{color:var(--color-text-muted);text-decoration:line-through;text-decoration-color:var(--color-primary)}
.competency-ft{padding:var(--s4) var(--s6);border-top:1px solid var(--color-border);background:var(--color-bg)}

/* ============================================================
   20. LESSON LAYOUT & SIDEBAR
   ============================================================ */
.lesson-layout{display:grid;grid-template-columns:var(--sidebar-w) 1fr;max-width:var(--page-max);margin:0 auto;min-height:calc(100vh - var(--nav-h))}
.lesson-sidebar{position:sticky;top:calc(var(--nav-h) + 3px);height:calc(100vh - var(--nav-h) - 3px);overflow-y:auto;border-right:1px solid var(--color-border);background:var(--color-surface);padding:var(--s6) 0;scrollbar-width:thin;scrollbar-color:var(--color-border) transparent}
.lesson-sidebar::-webkit-scrollbar{width:4px}
.lesson-sidebar::-webkit-scrollbar-thumb{background:var(--color-border);border-radius:4px}
.sidebar-group-label{font-size:var(--text-xs);font-weight:700;letter-spacing:0.10em;text-transform:uppercase;color:var(--color-text-light);padding:var(--s2) var(--s6);margin-bottom:var(--s1);margin-top:var(--s4)}
.sidebar-group-label:first-child{margin-top:0}
.sidebar-item{display:flex;align-items:center;gap:var(--s3);padding:var(--s2) var(--s6);font-size:var(--text-sm);color:var(--color-text-muted);cursor:pointer;transition:all var(--t-fast);text-decoration:none;border-left:3px solid transparent;line-height:1.375}
.sidebar-item:hover{color:var(--color-primary);background:var(--color-primary-light);text-decoration:none}
.sidebar-item.active{color:var(--color-primary);background:var(--color-primary-light);border-left-color:var(--color-primary);font-weight:500}
.sidebar-dot{width:6px;height:6px;border-radius:50%;background:var(--color-border-mid);flex-shrink:0;transition:background var(--t-fast)}
.sidebar-item.active .sidebar-dot{background:var(--color-primary)}
.lesson-main{min-width:0;padding:var(--s8) var(--s10) var(--s16)}

/* ============================================================
   21. LESSON SECTION HEADERS
   ============================================================ */
.lv-section{margin-bottom:var(--s10)}
.lv-section-hd{display:flex;align-items:center;gap:var(--s3);margin-bottom:var(--s6);padding-bottom:var(--s4);border-bottom:2px solid var(--color-border)}
.lv-section-icon{font-size:1.5rem;flex-shrink:0}
.lv-section-title{font-size:var(--text-2xl);font-weight:700;color:var(--color-text-primary);letter-spacing:-0.02em}
.lv-section-badge{margin-left:auto;font-size:var(--text-xs);font-weight:600;background:var(--color-primary-light);color:var(--color-primary);padding:var(--s1) var(--s3);border-radius:var(--r-full)}

/* ============================================================
   21b. NATIVE EMOJI ICON SYSTEM
   Icons are plain-text emoji glyphs, not image assets — this is
   what keeps them uniform in size, crisp at any resolution, and
   automatically correct in both light and dark mode with zero
   extra theming work.
   ============================================================ */
.lv-icon-feature{font-size:2.75rem;line-height:1;display:block;text-align:center;margin:0 auto var(--s3)}
.lv-icon-h1{margin-right:.2em}

/* ============================================================
   22. TABLES
   ============================================================ */
.tbl-wrap{width:100%;overflow-x:auto;border-radius:var(--r-lg);border:1px solid var(--color-border);box-shadow:var(--shadow-sm);margin-bottom:var(--s6)}
.lv-table{width:100%;border-collapse:collapse}
.lv-table thead{background:var(--color-primary-light)}
.lv-table th{padding:var(--s3) var(--s5);text-align:left;font-size:var(--text-sm);font-weight:600;color:var(--color-primary);letter-spacing:0.03em;white-space:nowrap}
.lv-table td{padding:var(--s3) var(--s5);font-size:var(--text-sm);color:var(--color-text-body);border-top:1px solid var(--color-border);line-height:1.625}
.lv-table tbody tr:hover{background:var(--color-bg)}
.lv-table td.hl{color:var(--color-primary);font-weight:600}
.lv-table td.abnormal{color:var(--color-danger);font-weight:600}

/* ============================================================
   23. PROCEDURE STEPS
   ============================================================ */
.steps{display:flex;flex-direction:column;gap:var(--s1)}
.step{display:flex;gap:var(--s4);padding:var(--s4) 0;position:relative}
.step:not(:last-child)::after{content:'';position:absolute;left:17px;top:calc(var(--s4) + 34px);bottom:0;width:2px;background:linear-gradient(to bottom,var(--color-primary-mid),var(--color-border))}
.step-num{width:34px;height:34px;border-radius:50%;background:var(--color-primary);color:white;font-size:var(--text-sm);font-weight:700;display:flex;align-items:center;justify-content:center;flex-shrink:0;z-index:1;box-shadow:0 0 0 4px var(--color-primary-light)}
.step-content{flex:1;padding-top:var(--s2)}
.step-title{font-size:var(--text-base);font-weight:600;color:var(--color-text-primary);margin-bottom:var(--s2)}
.step-body{font-size:var(--text-sm);color:var(--color-text-body);line-height:1.625}

/* ============================================================
   24. SEARCH OVERLAY
   ============================================================ */
.search-overlay{display:none;position:fixed;inset:0;background:rgba(0,0,0,0.50);z-index:2000;backdrop-filter:blur(4px);-webkit-backdrop-filter:blur(4px);align-items:flex-start;justify-content:center;padding-top:10vh}
.search-overlay.open{display:flex;animation:fadeIn var(--t-base)}
.search-modal{background:var(--color-surface);border-radius:var(--r-xl);width:100%;max-width:600px;margin-inline:var(--s4);box-shadow:var(--shadow-xl);overflow:hidden}
.search-input-row{display:flex;align-items:center;gap:var(--s3);padding:var(--s4) var(--s5);border-bottom:1px solid var(--color-border)}
.search-input-icon{font-size:1.25rem;color:var(--color-text-muted);flex-shrink:0}
.search-input{flex:1;border:none;background:none;font-size:var(--text-lg);color:var(--color-text-primary);outline:none;font-family:inherit}
.search-input::placeholder{color:var(--color-text-light)}
.search-close{font-size:var(--text-sm);color:var(--color-text-muted);background:var(--color-bg);border:1px solid var(--color-border);border-radius:var(--r-sm);padding:var(--s1) var(--s2);cursor:pointer;font-family:inherit}
.search-results{padding:var(--s4);max-height:60vh;overflow-y:auto}
.search-result{display:flex;align-items:flex-start;gap:var(--s3);padding:var(--s3) var(--s4);border-radius:var(--r-md);cursor:pointer;transition:background var(--t-fast);text-decoration:none}
.search-result:hover{background:var(--color-primary-light);text-decoration:none}
.search-result-title{font-size:var(--text-sm);font-weight:500;color:var(--color-text-primary)}
.search-result-sub{font-size:var(--text-xs);color:var(--color-text-muted)}
.search-empty{text-align:center;padding:var(--s8);color:var(--color-text-muted)}

/* ============================================================
   25. TOAST
   ============================================================ */
.toast-container{position:fixed;bottom:var(--s6);right:var(--s6);z-index:3000;display:flex;flex-direction:column;gap:var(--s2);pointer-events:none}
.toast{display:flex;align-items:center;gap:var(--s3);padding:var(--s4) var(--s5);background:var(--color-footer-bg);color:white;border-radius:var(--r-lg);box-shadow:var(--shadow-xl);font-size:var(--text-sm);font-weight:500;pointer-events:auto;animation:toastIn var(--t-base) ease;max-width:320px}
.toast.success{background:var(--color-success)}
.toast.warning{background:var(--color-warning)}
.toast.error  {background:var(--color-danger)}
.toast.info   {background:var(--color-primary)}
.toast.leaving{animation:toastOut var(--t-base) ease forwards}

/* ============================================================
   26. BACK TO TOP
   ============================================================ */
.back-to-top{position:fixed;bottom:var(--s8);right:var(--s8);width:44px;height:44px;border-radius:50%;background:var(--color-primary);color:white;display:flex;align-items:center;justify-content:center;cursor:pointer;box-shadow:var(--shadow-lg);opacity:0;visibility:hidden;transition:all var(--t-base);z-index:500;border:none;font-size:1.1rem}
.back-to-top.visible{opacity:1;visibility:visible}
.back-to-top:hover{background:var(--color-primary-dark);transform:translateY(-2px)}

/* ============================================================
   27. FOOTER
   ============================================================ */
.footer{background:var(--color-footer-bg);color:rgba(255,255,255,0.70);padding-block:var(--s16) var(--s8)}
.footer-grid{display:grid;grid-template-columns:2fr 1fr 1fr 1fr;gap:var(--s12);margin-bottom:var(--s12)}
.footer-logo{font-size:var(--text-xl);font-weight:800;color:white;letter-spacing:-0.03em;display:block;margin-bottom:var(--s3)}
.footer-logo span{color:#60A5FA}
.footer-desc{font-size:var(--text-sm);line-height:1.625;color:rgba(255,255,255,0.55);margin-bottom:var(--s5)}
.footer-col-title{font-size:var(--text-sm);font-weight:700;color:white;letter-spacing:0.05em;text-transform:uppercase;margin-bottom:var(--s4)}
.footer-links{display:flex;flex-direction:column;gap:var(--s3)}
.footer-link{font-size:var(--text-sm);color:rgba(255,255,255,0.55);text-decoration:none;transition:color var(--t-fast)}
.footer-link:hover{color:white;text-decoration:none}
.footer-bottom{display:grid;grid-template-columns:1fr auto 1fr;align-items:center;padding-top:var(--s8);border-top:1px solid rgba(255,255,255,0.10);gap:var(--s4)}
.footer-bottom-text{font-size:var(--text-sm);color:rgba(255,255,255,0.45);justify-self:start}
.footer-aboutme{justify-self:center;display:inline-flex;align-items:center;gap:6px;font-size:var(--text-sm);color:rgba(255,255,255,0.55);text-decoration:none;white-space:nowrap}
.footer-aboutme:hover{color:white}
.footer-aboutme img{width:18px;height:18px;border-radius:50%;object-fit:cover;vertical-align:middle}
.footer-bottom-links{display:flex;gap:var(--s6);justify-self:end}

/* ============================================================
   21c. FOOTER CREDIT — signature card (avatar + name + copyright)
   ============================================================ */
.footer-credit{display:flex;align-items:center;justify-content:space-between;gap:var(--s6);flex-wrap:wrap;background:#0A0A0F;border:1px solid rgba(255,255,255,0.08);border-radius:var(--r-xl);padding:var(--s5) var(--s7);margin-top:var(--s8)}
.footer-credit-id{display:flex;align-items:center;gap:var(--s4);text-decoration:none}
.footer-credit-id:hover .footer-credit-name{color:#fff}
.footer-credit-id:hover .footer-credit-handle{color:#fff}
.footer-credit-avatar{width:56px;height:56px;border-radius:50%;object-fit:cover;flex-shrink:0;border:2px solid rgba(255,255,255,0.15)}
.footer-credit-text{display:flex;flex-direction:column;gap:2px}
.footer-credit-name{font-size:var(--text-lg);font-weight:700;color:#fff;letter-spacing:-0.01em;transition:color var(--t-fast)}
.footer-credit-handle{font-size:var(--text-sm);font-weight:600;color:#F0B429;transition:color var(--t-fast)}
.footer-credit-right{display:flex;flex-direction:column;align-items:flex-end;gap:var(--s2)}
.footer-credit-copy{font-size:var(--text-sm);color:rgba(255,255,255,0.55);text-align:right}
.footer-credit-links{display:flex;gap:var(--s5)}
.footer-credit-links a{font-size:var(--text-xs);color:rgba(255,255,255,0.45);text-decoration:none}
.footer-credit-links a:hover{color:#fff}
@media (max-width:640px){
  .footer-credit{flex-direction:column;align-items:flex-start;text-align:left}
  .footer-credit-right{align-items:flex-start}
  .footer-credit-copy{text-align:left}
}

/* ============================================================
   28. REFERENCE VALUES
   ============================================================ */
.ref-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(190px,1fr));gap:var(--s3)}
.ref-item{background:var(--color-bg);border-radius:var(--r-md);padding:var(--s4);border:1px solid var(--color-border);text-align:center}
.ref-param{font-size:var(--text-xs);color:var(--color-text-muted);text-transform:uppercase;letter-spacing:0.06em;margin-bottom:var(--s2);font-weight:500}
.ref-range{font-size:var(--text-lg);font-weight:700;color:var(--color-text-primary)}
.ref-unit{font-size:var(--text-xs);color:var(--color-text-muted);margin-top:var(--s1)}

/* ============================================================
   29. REVISION CARDS
   ============================================================ */
.revision-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(250px,1fr));gap:var(--s4)}
.revision-card{background:var(--color-surface);border-radius:var(--r-xl);border:1px solid var(--color-border);padding:var(--s6);box-shadow:var(--shadow-sm);transition:all var(--t-base);position:relative;overflow:hidden}
.revision-card::before{content:'';position:absolute;top:0;left:0;right:0;height:4px;background:var(--color-primary)}
.revision-card:hover{box-shadow:var(--shadow-lg);transform:translateY(-2px)}
.revision-card-n{font-size:var(--text-xs);font-weight:700;color:var(--color-primary);letter-spacing:0.08em;text-transform:uppercase;margin-bottom:var(--s3)}
.revision-card-body{font-size:var(--text-sm);color:var(--color-text-body);line-height:1.625}

/* ============================================================
   30. LESSON NAV FOOTER
   ============================================================ */
.lesson-nav-footer{display:grid;grid-template-columns:1fr 1fr;gap:var(--s4);margin-top:var(--s12);padding-top:var(--s8);border-top:2px solid var(--color-border)}
.lesson-nav-card{background:var(--color-surface);border-radius:var(--r-xl);border:1px solid var(--color-border);padding:var(--s5);text-decoration:none;display:flex;flex-direction:column;gap:var(--s2);transition:all var(--t-base)}
.lesson-nav-card:hover{border-color:var(--color-primary-mid);box-shadow:var(--shadow-md);text-decoration:none}
.lesson-nav-card.next{text-align:right}
.lesson-nav-dir{font-size:var(--text-xs);font-weight:600;color:var(--color-text-muted);letter-spacing:0.06em;text-transform:uppercase;display:flex;align-items:center;gap:var(--s1)}
.lesson-nav-card.next .lesson-nav-dir{justify-content:flex-end}
.lesson-nav-title{font-size:var(--text-base);font-weight:600;color:var(--color-text-primary);line-height:1.375}

/* ============================================================
   30b. PAGE HERO (utility pages: about, contact, subjects,
   search, progress, calculators, privacy, terms, bookmarks)
   Same light-to-surface wash as .hero/.subject-banner, so it
   inherits the same dark-mode treatment instead of hardcoding
   a light-only gradient that goes muddy/illegible in dark mode.
   ============================================================ */
.page-hero{background:linear-gradient(135deg,var(--color-primary-light) 0%,var(--color-surface) 100%);padding:var(--s16) 0 var(--s12);border-bottom:1px solid var(--color-border)}
.page-hero-lg{padding:var(--s20) 0 var(--s16)}
.page-hero-center{text-align:center}
[data-theme="dark"] .page-hero{background:linear-gradient(135deg,#0d1f3c 0%,var(--color-bg) 60%)}

/* ============================================================
   31. SUBJECT BANNER
   ============================================================ */
.subject-banner{padding:var(--s16) 0 var(--s12);background:linear-gradient(135deg,var(--color-primary-light) 0%,#fff 100%);border-bottom:1px solid var(--color-border)}
[data-theme="dark"] .subject-banner{background:linear-gradient(135deg,#0d1f3c 0%,var(--color-bg) 100%)}
.subject-banner-inner{display:flex;align-items:flex-start;gap:var(--s8)}
.subject-banner-icon{width:80px;height:80px;border-radius:var(--r-xl);background:var(--color-primary);display:flex;align-items:center;justify-content:center;font-size:2.5rem;flex-shrink:0;box-shadow:var(--shadow-lg)}
.subject-banner-stats{display:flex;gap:var(--s8);flex-wrap:wrap;margin-top:var(--s5)}
.subject-stat-n{font-size:var(--text-2xl);font-weight:800;color:var(--color-primary);display:block}
.subject-stat-l{font-size:var(--text-xs);color:var(--color-text-muted);text-transform:uppercase;letter-spacing:0.06em}

/* ============================================================
   32. FILTER BAR
   ============================================================ */
.filter-bar{background:var(--color-surface);border:1px solid var(--color-border);border-radius:var(--r-xl);padding:var(--s4) var(--s5);display:flex;align-items:center;gap:var(--s4);flex-wrap:wrap;margin-bottom:var(--s6);box-shadow:var(--shadow-sm)}
.filter-group{display:flex;align-items:center;gap:var(--s2)}
.filter-label{font-size:var(--text-xs);font-weight:700;color:var(--color-text-muted);letter-spacing:0.06em;text-transform:uppercase;white-space:nowrap}
.filter-btn{padding:var(--s1) var(--s3);border-radius:var(--r-full);font-size:var(--text-xs);font-weight:500;color:var(--color-text-muted);background:var(--color-bg);border:1px solid var(--color-border);cursor:pointer;transition:all var(--t-fast);font-family:inherit}
.filter-btn:hover,.filter-btn.active{background:var(--color-primary);border-color:var(--color-primary);color:white}
.inline-search{display:flex;align-items:center;gap:var(--s2);background:var(--color-bg);border:1px solid var(--color-border);border-radius:var(--r-full);padding:var(--s2) var(--s4);flex:1;min-width:200px}
.inline-search input{border:none;background:none;font-size:var(--text-sm);color:var(--color-text-primary);outline:none;width:100%;font-family:inherit}
.inline-search input::placeholder{color:var(--color-text-light)}

/* ============================================================
   33. PROGRESS DASHBOARD
   ============================================================ */
.progress-stats{display:grid;grid-template-columns:repeat(auto-fill,minmax(200px,1fr));gap:var(--s4);margin-bottom:var(--s8)}
.progress-stat-card{background:var(--color-surface);border-radius:var(--r-xl);border:1px solid var(--color-border);padding:var(--s6);box-shadow:var(--shadow-sm);text-align:center}
.progress-stat-v{font-size:var(--text-4xl);font-weight:800;color:var(--color-primary);letter-spacing:-0.03em;display:block;line-height:1;margin-bottom:var(--s2)}
.progress-stat-l{font-size:var(--text-sm);color:var(--color-text-muted)}

/* ============================================================
   34. BOOKMARKS
   ============================================================ */
.bookmarks-empty{text-align:center;padding:var(--s20);color:var(--color-text-muted)}
.bookmarks-empty-icon{font-size:4rem;margin-bottom:var(--s4);opacity:.25}

/* ============================================================
   35. 404
   ============================================================ */
.error-page{min-height:calc(100vh - var(--nav-h));display:flex;align-items:center;justify-content:center;text-align:center;padding:var(--s12)}
.error-code{font-size:clamp(6rem,20vw,12rem);font-weight:800;line-height:1;letter-spacing:-0.05em;background:linear-gradient(135deg,var(--color-primary),var(--color-accent));-webkit-background-clip:text;-webkit-text-fill-color:transparent;background-clip:text;display:block;margin-bottom:var(--s4)}

/* ============================================================
   36. CONTACT FORM
   ============================================================ */
.contact-form{background:var(--color-surface);border-radius:var(--r-2xl);border:1px solid var(--color-border);padding:var(--s10);box-shadow:var(--shadow-lg)}
.form-group{margin-bottom:var(--s5)}
.form-label{display:block;font-size:var(--text-sm);font-weight:600;color:var(--color-text-primary);margin-bottom:var(--s2)}
.form-input,.form-select,.form-textarea{width:100%;padding:var(--s3) var(--s4);border:2px solid var(--color-border);border-radius:var(--r-md);font-size:var(--text-base);font-family:inherit;color:var(--color-text-primary);background:var(--color-bg);transition:border-color var(--t-fast),box-shadow var(--t-fast);outline:none}
.form-input:focus,.form-select:focus,.form-textarea:focus{border-color:var(--color-primary);box-shadow:0 0 0 3px rgba(37,99,235,0.10);background:var(--color-surface)}
.form-textarea{resize:vertical;min-height:140px;line-height:1.625}
.form-grid{display:grid;grid-template-columns:1fr 1fr;gap:var(--s5)}
.form-success{text-align:center;padding:var(--s8);display:none}
.form-success.show{display:block;animation:fadeIn var(--t-base)}
.form-error{text-align:center;padding:var(--s8)}
.form-error[hidden]{display:none}

/* ============================================================
   37. ANIMATIONS
   ============================================================ */
@keyframes fadeIn   {from{opacity:0;transform:translateY(8px)}to{opacity:1;transform:translateY(0)}}
@keyframes slideDown{from{opacity:0;transform:translateY(-10px)}to{opacity:1;transform:translateY(0)}}
@keyframes toastIn  {from{opacity:0;transform:translateX(100%)}to{opacity:1;transform:translateX(0)}}
@keyframes toastOut {from{opacity:1;transform:translateX(0)}to{opacity:0;transform:translateX(100%)}}
@keyframes spin     {to{transform:rotate(360deg)}}

.reveal{opacity:0;transform:translateY(20px);transition:opacity .6s ease,transform .6s ease}
.reveal.visible{opacity:1;transform:translateY(0)}
.spinner{width:32px;height:32px;border:3px solid var(--color-border);border-top-color:var(--color-primary);border-radius:50%;animation:spin .8s linear infinite}

/* ============================================================
   38. UTILITIES
   ============================================================ */
.hidden  {display:none !important}
.sr-only {position:absolute;width:1px;height:1px;padding:0;margin:-1px;overflow:hidden;clip:rect(0,0,0,0);white-space:nowrap;border:0}
.divider {height:1px;background:var(--color-border);margin-block:var(--s8)}
.text-center{text-align:center}
.text-muted{color:var(--color-text-muted)}
.text-blue{color:var(--color-primary)}

/* ============================================================
   38b. ACCESSIBILITY — skip link + focus visibility (WCAG 2.2 AA)
   ============================================================ */
.skip-link{
  position:absolute;top:-40px;left:0;z-index:1000;
  background:var(--color-primary);color:#fff;
  padding:var(--s3) var(--s5);border-radius:0 0 var(--r-md) 0;
  font-weight:700;text-decoration:none;transition:top var(--t-fast);
}
.skip-link:focus{top:0}

/* Consistent, visible keyboard focus outline across all interactive elements.
   Uses :focus-visible so mouse/touch users don't see a ring on click,
   while keyboard users always get a clear indicator. */
a:focus-visible,
button:focus-visible,
input:focus-visible,
select:focus-visible,
textarea:focus-visible,
[tabindex]:focus-visible{
  outline:3px solid var(--color-primary);
  outline-offset:2px;
  border-radius:2px;
}
.font-bold{font-weight:700}
.mb-4{margin-bottom:var(--s4)} .mb-6{margin-bottom:var(--s6)} .mb-8{margin-bottom:var(--s8)}
.mt-6{margin-top:var(--s6)}   .mt-8{margin-top:var(--s8)}
.ml-auto{margin-left:auto}
.flex{display:flex} .items-center{align-items:center} .gap-3{gap:var(--s3)} .gap-4{gap:var(--s4)}
.tag{display:inline-flex;align-items:center;gap:var(--s1);padding:var(--s1) var(--s3);background:var(--color-primary-light);border:1px solid var(--color-primary-mid);color:var(--color-primary);border-radius:var(--r-full);font-size:var(--text-xs);font-weight:500}

/* ============================================================
   39. RESPONSIVE — TABLET
   ============================================================ */
@media(max-width:1024px){
  .lesson-layout{grid-template-columns:1fr}
  .lesson-sidebar{display:none}
  .footer-grid{grid-template-columns:1fr 1fr;gap:var(--s8)}
  .lesson-main{padding:var(--s6) var(--s6) var(--s12)}
}

/* ============================================================
   40. RESPONSIVE — MOBILE
   ============================================================ */
@media(max-width:768px){
  :root{--nav-h:60px}
  .nav-links{display:none}
  .nav-mobile-btn{display:flex}
  h1{font-size:var(--text-3xl)} h2{font-size:var(--text-2xl)}
  .container,.container-narrow{padding-inline:var(--s4)}
  .hero{padding-block:var(--s16) var(--s12)}
  .hero-stats{gap:var(--s8)}
  .form-grid{grid-template-columns:1fr}
  .footer-grid{grid-template-columns:1fr;gap:var(--s8)}
  .footer-bottom{grid-template-columns:1fr;justify-items:center;text-align:center}
  .footer-bottom-text,.footer-aboutme,.footer-bottom-links{justify-self:center}
  .lesson-nav-footer{grid-template-columns:1fr}
  .contact-form{padding:var(--s6)}
  .quiz-tf{grid-template-columns:1fr}
  .lesson-hero{padding:var(--s8) 0 var(--s6)}
  .flashcard-grid{grid-template-columns:1fr}
  .revision-grid{grid-template-columns:1fr}
  .progress-stats{grid-template-columns:1fr 1fr}
  .subject-banner-inner{flex-direction:column}
  .lesson-main{padding:var(--s4) var(--s4) var(--s10)}
  .back-to-top{right:var(--s4);bottom:var(--s6)}
  .toast-container{right:var(--s4);left:var(--s4)}
  .toast{max-width:100%}
  .case-result-grid{grid-template-columns:1fr 1fr}
  .quiz-match{grid-template-columns:1fr}
}
@media(max-width:480px){
  .hero-title{font-size:1.75rem}
  .progress-stats{grid-template-columns:1fr}
  .filter-bar{flex-direction:column;align-items:flex-start}
  .inline-search{width:100%}
  .ref-grid{grid-template-columns:1fr 1fr}
}

/* ============================================================
   41. PRINT
   ============================================================ */
@media print{
  .nav,.reading-progress,.back-to-top,.lesson-sidebar,.toast-container,.nav-mobile-menu{display:none !important}
  .page-body{padding-top:0}
  .lesson-layout{display:block}
  .accordion-content{max-height:none !important}
  body{font-size:12pt;color:#000}
  .lesson-hero{background:none !important;color:#000 !important}
  .lesson-hero h1{color:#000 !important}
}

/* ============================================================
   42. REDUCE MOTION
   ============================================================ */
@media(prefers-reduced-motion:reduce){
  *,*::before,*::after{animation-duration:.01ms !important;transition-duration:.01ms !important}
  html{scroll-behavior:auto}
}


/* ============================================================
   23. BRAND LOGO — image wordmark, legible on any surface
   ============================================================ */
.logo-chip{display:inline-flex;align-items:center;background:#FFFFFF;border-radius:var(--r-md);padding:6px 12px;box-shadow:0 1px 3px rgba(0,0,0,0.08);line-height:0}
.nav-logo{display:inline-flex;align-items:center}
.nav-logo .logo-chip{padding:5px 10px}
.logo-img{height:26px;width:auto;display:block}
.footer-logo.logo-chip{margin-bottom:var(--s3)}
.footer-logo .logo-img{height:24px}

/* ============================================================
   43. DARK MODE — CALLOUT TEXT REFINEMENT
   Light-mode callouts (info/warning/danger/success/tip cards,
   quiz feedback) use deliberately dark, saturated text for
   contrast against pastel backgrounds. Now that those backgrounds
   are muted dark washes (see --color-*-light overrides above),
   the same hex values are recast as soft, legible tints so
   nothing glares or muddies against the dark page.
   ============================================================ */
[data-theme="dark"] .info-card.info    .info-title,
[data-theme="dark"] .info-card.info    .info-text{color:#67E8F9}
[data-theme="dark"] .info-card.warning .info-title,
[data-theme="dark"] .info-card.warning .info-text{color:#FCD34D}
[data-theme="dark"] .info-card.danger  .info-title,
[data-theme="dark"] .info-card.danger  .info-text{color:#FCA5A5}
[data-theme="dark"] .info-card.success .info-title,
[data-theme="dark"] .info-card.success .info-text{color:#6EE7B7}
[data-theme="dark"] .info-card.tip     .info-title,
[data-theme="dark"] .info-card.tip     .info-text{color:#C4B5FD}

[data-theme="dark"] .lab-tip{border-left-color:#A78BFA}
[data-theme="dark"] .lab-tip-hd{color:#C4B5FD}
[data-theme="dark"] .lab-tip-body{color:#DDD6FE}

[data-theme="dark"] .warning-card-hd{color:#FCA5A5}
[data-theme="dark"] .warning-card-body{color:#FECACA}

[data-theme="dark"] .summary-card-hd{color:#6EE7B7}
[data-theme="dark"] .summary-list li{color:#A7F3D0}

[data-theme="dark"] .quiz-feedback.correct{color:#6EE7B7}
[data-theme="dark"] .quiz-feedback.incorrect{color:#FCA5A5}

/* Case-study "lab tip" icon backdrop and other small fixed-color
   chips read as slightly too neon on dark surfaces — soften. */
[data-theme="dark"] .subject-banner-icon{box-shadow:0 8px 32px rgba(0,0,0,0.45)}