/* ============================================================
   ALGO_CORE — Shared Design System
   Source of truth: DESIGN.md "Academic Precision" theme
   ============================================================ */

/* Google Fonts */
@import url('https://fonts.googleapis.com/css2?family=JetBrains+Mono:wght@400;500;600;700&family=IBM+Plex+Sans:wght@300;400;500;600&display=swap');
@import url('https://fonts.googleapis.com/css2?family=Material+Symbols+Outlined:opsz,wght,FILL,GRAD@20..48,100..700,0..1,-50..200&display=swap');

/* ── Color Tokens ─────────────────────────────────────────── */
:root {
  --color-surface:                 #fff8f1;
  --color-surface-dim:             #e6d9be;
  --color-surface-bright:          #fff8f1;
  --color-surface-container-lowest:#ffffff;
  --color-surface-container-low:   #fff2db;
  --color-surface-container:       #fbecd1;
  --color-surface-container-high:  #f5e7cb;
  --color-surface-container-highest:#efe1c6;
  --color-on-surface:              #211b0a;
  --color-on-surface-variant:      #55433a;
  --color-inverse-surface:         #37301d;
  --color-inverse-on-surface:      #feefd4;
  --color-outline:                 #897268;
  --color-outline-variant:         #dcc1b5;
  --color-surface-tint:            #9b4511;
  --color-primary:                 #97430e;
  --color-on-primary:              #ffffff;
  --color-primary-container:       #b75a26;
  --color-on-primary-container:    #fffbff;
  --color-primary-fixed:           #ffdbcb;
  --color-primary-fixed-dim:       #ffb692;
  --color-on-primary-fixed:        #341100;
  --color-on-primary-fixed-variant:#793000;
  --color-inverse-primary:         #ffb692;
  --color-secondary:               #675d4e;
  --color-on-secondary:            #ffffff;
  --color-secondary-container:     #ebdecb;
  --color-on-secondary-container:  #6b6152;
  --color-tertiary:                #4c6244;
  --color-on-tertiary:             #ffffff;
  --color-tertiary-container:      #647b5c;
  --color-on-tertiary-container:   #f8fff0;
  --color-tertiary-fixed:          #d0eac4;
  --color-tertiary-fixed-dim:      #b4cea9;
  --color-error:                   #ba1a1a;
  --color-on-error:                #ffffff;
  --color-error-container:         #ffdad6;
  --color-background:              #fff8f1;
  --color-on-background:           #211b0a;
  --color-surface-variant:         #efe1c6;

  /* Semantic aliases */
  --tan-border:                    #e4dcc8;
  --card-bg:                       #ffffff;
  --card-radius:                   12px;

  /* ── Typography Tokens ────────────────────────────────── */
  --font-mono:        'JetBrains Mono', monospace;
  --font-sans:        'IBM Plex Sans', sans-serif;

  /* Headline sizes */
  --text-headline-lg-size:   32px;
  --text-headline-lg-lh:     40px;
  --text-headline-lg-weight: 600;
  --text-headline-lg-ls:     -0.02em;

  --text-headline-md-size:   24px;
  --text-headline-md-lh:     32px;
  --text-headline-md-weight: 500;

  --text-headline-sm-size:   18px;
  --text-headline-sm-lh:     24px;
  --text-headline-sm-weight: 500;

  /* Display (extra large hero) */
  --text-display-lg-size:   64px;
  --text-display-lg-lh:     1.1;
  --text-display-lg-weight: 300;
  --text-display-lg-ls:     -0.02em;

  /* Body */
  --text-body-lg-size:    18px;
  --text-body-lg-lh:      28px;

  --text-body-md-size:    16px;
  --text-body-md-lh:      24px;

  --text-body-sm-size:    14px;
  --text-body-sm-lh:      20px;

  /* Labels */
  --text-label-md-size:    14px;
  --text-label-md-lh:      16px;
  --text-label-md-weight:  500;
  --text-label-md-ls:      0.05em;

  --text-label-sm-size:    12px;
  --text-label-sm-lh:      14px;
  --text-label-sm-weight:  400;

  --text-label-caps-size:   12px;
  --text-label-caps-lh:     1.0;
  --text-label-caps-weight: 700;
  --text-label-caps-ls:     0.1em;

  /* ── Spacing Tokens ──────────────────────────────────── */
  --space-1:  4px;
  --space-2:  8px;
  --space-3:  12px;
  --space-4:  16px;
  --space-5:  20px;
  --space-6:  24px;
  --space-8:  32px;
  --space-10: 40px;
  --space-12: 48px;
  --space-16: 64px;
  --space-20: 80px;
  --space-30: 120px;

  --gutter:           24px;
  --margin-mobile:    16px;
  --margin-desktop:   48px;
  --container-max:    1120px;

  /* ── Border Radius ───────────────────────────────────── */
  --radius-sm:   4px;
  --radius-md:   8px;
  --radius-lg:   12px;
  --radius-xl:   16px;
  --radius-full: 9999px;

  /* ── Shadows ─────────────────────────────────────────── */
  --shadow-card:     0 2px 4px rgba(43, 36, 24, 0.05);
  --shadow-elevated: 0 4px 12px rgba(43, 36, 24, 0.10);
  --shadow-lg:       0 8px 24px rgba(43, 36, 24, 0.12);
}

/* ── Reset & Base ────────────────────────────────────────── */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-sans);
  font-size: var(--text-body-md-size);
  line-height: var(--text-body-md-lh);
  color: var(--color-on-surface);
  background-color: var(--color-surface);
  -webkit-font-smoothing: antialiased;
  overflow-x: hidden;
}

img { max-width: 100%; height: auto; display: block; }
a { color: inherit; text-decoration: none; }
button { cursor: pointer; font-family: inherit; border: none; background: none; }
ul, ol { list-style: none; }
input, button, a { outline: none; }

/* Keyboard focus states (required) */
a:focus-visible,
button:focus-visible,
input:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
  border-radius: var(--radius-sm);
}

/* ── Material Symbols ────────────────────────────────────── */
.material-symbols-outlined {
  font-family: 'Material Symbols Outlined';
  font-weight: normal;
  font-style: normal;
  font-size: 24px;
  line-height: 1;
  letter-spacing: normal;
  text-transform: none;
  display: inline-block;
  white-space: nowrap;
  word-wrap: normal;
  direction: ltr;
  font-variation-settings: 'FILL' 0, 'wght' 400, 'GRAD' 0, 'opsz' 24;
  vertical-align: middle;
  user-select: none;
}

/* ── Typography Utility Classes ─────────────────────────── */
.font-mono { font-family: var(--font-mono); }
.font-sans  { font-family: var(--font-sans);  }

.text-display-lg {
  font-family: var(--font-sans);
  font-size: var(--text-display-lg-size);
  line-height: var(--text-display-lg-lh);
  font-weight: var(--text-display-lg-weight);
  letter-spacing: var(--text-display-lg-ls);
}
.text-headline-lg {
  font-family: var(--font-mono);
  font-size: var(--text-headline-lg-size);
  line-height: var(--text-headline-lg-lh);
  font-weight: var(--text-headline-lg-weight);
  letter-spacing: var(--text-headline-lg-ls);
}
.text-headline-md {
  font-family: var(--font-mono);
  font-size: var(--text-headline-md-size);
  line-height: var(--text-headline-md-lh);
  font-weight: var(--text-headline-md-weight);
}
.text-headline-sm {
  font-family: var(--font-mono);
  font-size: var(--text-headline-sm-size);
  line-height: var(--text-headline-sm-lh);
  font-weight: var(--text-headline-sm-weight);
}
.text-body-lg {
  font-family: var(--font-sans);
  font-size: var(--text-body-lg-size);
  line-height: var(--text-body-lg-lh);
  font-weight: 400;
}
.text-body-md {
  font-family: var(--font-sans);
  font-size: var(--text-body-md-size);
  line-height: var(--text-body-md-lh);
  font-weight: 400;
}
.text-body-sm {
  font-family: var(--font-sans);
  font-size: var(--text-body-sm-size);
  line-height: var(--text-body-sm-lh);
  font-weight: 400;
}
.text-label-md {
  font-family: var(--font-mono);
  font-size: var(--text-label-md-size);
  line-height: var(--text-label-md-lh);
  font-weight: var(--text-label-md-weight);
  letter-spacing: var(--text-label-md-ls);
}
.text-label-sm {
  font-family: var(--font-mono);
  font-size: var(--text-label-sm-size);
  line-height: var(--text-label-sm-lh);
  font-weight: var(--text-label-sm-weight);
}
.text-label-caps {
  font-family: var(--font-mono);
  font-size: var(--text-label-caps-size);
  line-height: var(--text-label-caps-lh);
  font-weight: var(--text-label-caps-weight);
  letter-spacing: var(--text-label-caps-ls);
  text-transform: uppercase;
}

/* Color helpers */
.color-primary         { color: var(--color-primary); }
.color-on-surface      { color: var(--color-on-surface); }
.color-on-surface-var  { color: var(--color-on-surface-variant); }
.color-secondary       { color: var(--color-secondary); }
.color-outline         { color: var(--color-outline); }

/* ── Layout Utilities ────────────────────────────────────── */
.container {
  max-width: var(--container-max);
  margin-left: auto;
  margin-right: auto;
  padding-left: var(--margin-desktop);
  padding-right: var(--margin-desktop);
}

@media (max-width: 768px) {
  .container {
    padding-left: var(--margin-mobile);
    padding-right: var(--margin-mobile);
  }
}

/* ── Card Component ──────────────────────────────────────── */
.card {
  background: var(--card-bg);
  border: 1px solid var(--tan-border);
  border-radius: var(--card-radius);
  box-shadow: var(--shadow-card);
  transition: box-shadow 0.2s ease, transform 0.2s ease;
}
.card:hover {
  box-shadow: var(--shadow-elevated);
}
.card-interactive:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-elevated);
}

/* ── Button Components ───────────────────────────────────── */
.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  font-family: var(--font-mono);
  font-size: var(--text-label-md-size);
  font-weight: var(--text-label-md-weight);
  letter-spacing: var(--text-label-md-ls);
  text-transform: uppercase;
  border-radius: var(--radius-md);
  padding: var(--space-3) var(--space-6);
  transition: all 0.2s ease;
  cursor: pointer;
  text-decoration: none;
  border: none;
}
.btn:active { transform: scale(0.97); }

.btn-primary {
  background: var(--color-primary);
  color: var(--color-on-primary);
  border: 1px solid var(--color-primary);
}
.btn-primary:hover {
  background: #7a3609;
  border-color: #7a3609;
}
.btn-primary:focus-visible {
  outline: 2px solid var(--color-on-primary);
  outline-offset: 2px;
}

.btn-outline {
  background: transparent;
  color: var(--color-primary);
  border: 1px solid var(--color-primary);
}
.btn-outline:hover {
  background: var(--color-primary-fixed);
}

.btn-ghost {
  background: transparent;
  color: var(--color-on-surface-variant);
  border: 1px solid var(--tan-border);
}
.btn-ghost:hover {
  background: var(--color-surface-container);
}

/* ── Diamond Divider ─────────────────────────────────────── */
.diamond-divider {
  height: 1px;
  background: var(--tan-border);
  position: relative;
  margin: var(--space-12) 0;
}
.diamond-divider::after {
  content: '◆';
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  background: var(--color-surface);
  padding: 0 10px;
  color: var(--color-primary);
  font-size: 12px;
}

/* ── Navigation (Top Nav — Landing) ─────────────────────── */
.top-nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 100;
  height: 72px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 var(--margin-desktop);
  background: rgba(255, 248, 241, 0.9);
  backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--tan-border);
  transition: box-shadow 0.2s ease;
}
.top-nav.scrolled {
  box-shadow: var(--shadow-card);
}
.top-nav__logo {
  font-family: var(--font-mono);
  font-size: 20px;
  font-weight: 600;
  color: var(--color-on-surface);
  text-decoration: none;
  letter-spacing: -0.02em;
}
.top-nav__links {
  display: flex;
  align-items: center;
  gap: var(--space-8);
  margin-left: var(--space-12);
}
.top-nav__link {
  font-family: var(--font-mono);
  font-size: var(--text-label-caps-size);
  font-weight: var(--text-label-caps-weight);
  letter-spacing: var(--text-label-caps-ls);
  text-transform: uppercase;
  color: var(--color-secondary);
  text-decoration: none;
  transition: color 0.15s ease;
}
.top-nav__link:hover,
.top-nav__link.active { color: var(--color-primary); }
.top-nav__link.active {
  border-bottom: 2px solid var(--color-primary);
  padding-bottom: 2px;
}
.top-nav__search {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  border-bottom: 1px solid var(--color-outline);
  padding: var(--space-1) 0;
}
.top-nav__search input {
  background: transparent;
  border: none;
  font-family: var(--font-sans);
  font-size: var(--text-body-md-size);
  color: var(--color-on-surface);
  width: 180px;
}
.top-nav__search input::placeholder { color: var(--color-outline); }
.top-nav__actions {
  display: flex;
  align-items: center;
  gap: var(--space-4);
}
/* Hamburger */
.nav-hamburger {
  display: none;
  flex-direction: column;
  gap: 5px;
  cursor: pointer;
  padding: var(--space-2);
  background: none;
  border: none;
}
.nav-hamburger span {
  display: block;
  width: 22px;
  height: 2px;
  background: var(--color-on-surface);
  border-radius: 2px;
  transition: all 0.3s ease;
}

/* ── App Header (inner pages) ────────────────────────────── */
.app-header {
  position: sticky;
  top: 0;
  z-index: 100;
  height: 64px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 var(--gutter);
  background: var(--color-surface);
  border-bottom: 1px solid var(--color-outline-variant);
}
.app-header__left {
  display: flex;
  align-items: center;
  gap: var(--space-4);
}
.app-header__logo {
  font-family: var(--font-mono);
  font-size: 18px;
  font-weight: 600;
  color: var(--color-primary);
  letter-spacing: -0.02em;
  text-decoration: none;
}
.app-header__divider {
  width: 1px;
  height: 24px;
  background: var(--color-outline-variant);
}
.app-header__breadcrumb {
  font-family: var(--font-mono);
  font-size: var(--text-label-md-size);
  font-weight: var(--text-label-md-weight);
  letter-spacing: var(--text-label-md-ls);
  text-transform: uppercase;
  color: var(--color-on-surface-variant);
}
.app-header__right {
  display: flex;
  align-items: center;
  gap: var(--space-4);
}
/* Tab bar for theory/sandbox pages */
.tab-bar {
  display: flex;
  align-items: center;
  gap: var(--space-6);
}
.tab-bar__link {
  font-family: var(--font-mono);
  font-size: var(--text-label-md-size);
  font-weight: var(--text-label-md-weight);
  letter-spacing: var(--text-label-md-ls);
  text-transform: uppercase;
  color: var(--color-on-surface-variant);
  text-decoration: none;
  padding-bottom: 4px;
  border-bottom: 3px solid transparent;
  transition: color 0.15s ease, border-color 0.15s ease;
}
.tab-bar__link:hover { color: var(--color-primary); }
.tab-bar__link.active {
  color: var(--color-primary);
  font-weight: 700;
  border-bottom-color: var(--color-primary);
}

/* ── Sidebar (inner pages) ───────────────────────────────── */
.app-layout {
  display: flex;
  min-height: calc(100vh - 64px);
}
.sidebar {
  width: 220px;
  min-height: 100%;
  background: var(--color-surface-container-low);
  border-right: 1px solid var(--color-outline-variant);
  display: flex;
  flex-direction: column;
  padding: var(--space-4);
  flex-shrink: 0;
  position: sticky;
  top: 64px;
  height: calc(100vh - 64px);
  overflow-y: auto;
}
.sidebar__header {
  margin-bottom: var(--space-8);
}
.sidebar__module-title {
  font-family: var(--font-mono);
  font-size: var(--text-headline-sm-size);
  font-weight: var(--text-headline-sm-weight);
  color: var(--color-primary);
  margin-bottom: 2px;
}
.sidebar__module-sub {
  font-family: var(--font-mono);
  font-size: var(--text-label-sm-size);
  color: var(--color-on-surface-variant);
  opacity: 0.7;
}
.sidebar__nav {
  display: flex;
  flex-direction: column;
  gap: 4px;
  flex: 1;
}
.sidebar__link {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  padding: var(--space-3);
  border-radius: var(--radius-md);
  font-family: var(--font-mono);
  font-size: var(--text-label-md-size);
  font-weight: var(--text-label-md-weight);
  letter-spacing: var(--text-label-md-ls);
  color: var(--color-on-surface-variant);
  text-decoration: none;
  transition: background 0.15s ease, color 0.15s ease;
}
.sidebar__link:hover {
  background: var(--color-surface-variant);
  color: var(--color-on-surface);
}
.sidebar__link.active {
  background: var(--color-primary-fixed);
  border-left: 4px solid var(--color-primary);
  padding-left: calc(var(--space-3) - 4px);
  color: var(--color-primary);
  font-weight: 700;
}
.sidebar__footer {
  padding-top: var(--space-6);
  margin-top: auto;
}

/* Mobile sidebar toggle */
.sidebar-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.4);
  z-index: 90;
}
.sidebar-overlay.active { display: block; }
.sidebar-toggle {
  display: none;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  background: none;
  border: none;
  cursor: pointer;
  color: var(--color-on-surface);
}

/* ── Main Content Area ───────────────────────────────────── */
.main-content {
  flex: 1;
  overflow-y: auto;
  padding: var(--space-6);
  background: var(--color-background);
}
.content-wrap {
  max-width: var(--container-max);
  margin: 0 auto;
}

/* ── Stack Slot (Reactive Memory Matrix) ─────────────────── */
.stack-slot {
  position: relative;
  height: 52px;
  display: flex;
  align-items: center;
  justify-content: center;
  border: 1px dashed var(--tan-border);
  border-radius: var(--radius-md);
  font-family: var(--font-mono);
  font-size: 14px;
  font-weight: 400;
  transition: all 0.3s ease;
  background: var(--color-surface-container-lowest);
}
.stack-slot .slot-index {
  position: absolute;
  right: -48px;
  font-size: 11px;
  color: var(--color-outline-variant);
  font-family: var(--font-mono);
}
.stack-slot .slot-label {
  color: var(--color-outline-variant);
  opacity: 0.5;
  font-size: 12px;
}
.stack-slot.filled {
  border: 2px solid var(--color-primary);
  background: var(--color-surface-container-lowest);
  font-weight: 700;
  color: var(--color-on-surface);
  box-shadow: 0 2px 6px rgba(151, 67, 14, 0.12);
}
.stack-slot.filled .slot-label {
  color: var(--color-on-surface);
  opacity: 1;
}
/* Pop-in animation */
@keyframes popIn {
  0%   { transform: translateY(-12px) scale(0.9); opacity: 0; }
  60%  { transform: translateY(2px) scale(1.02); }
  100% { transform: translateY(0) scale(1); opacity: 1; }
}
/* Pop-out animation */
@keyframes popOut {
  0%   { transform: translateY(0) scale(1); opacity: 1; }
  100% { transform: translateY(-16px) scale(0.85); opacity: 0; }
}
.stack-slot.animate-in {
  animation: popIn 0.32s cubic-bezier(0.175, 0.885, 0.32, 1.275) forwards;
}
.stack-slot.animate-out {
  animation: popOut 0.22s ease-in forwards;
}

/* Top pointer */
.top-pointer {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  font-family: var(--font-mono);
  font-size: 13px;
  font-weight: 700;
  color: var(--color-primary);
  transition: transform 0.4s cubic-bezier(0.175, 0.885, 0.32, 1.275);
  white-space: nowrap;
}
.top-pointer.hidden-ptr { opacity: 0.3; }

/* ── Interactive Animation Panel ─────────────────────────── */
.anim-section {
  margin-bottom: var(--space-8);
}
.anim-section-title {
  font-family: var(--font-mono);
  font-size: var(--text-label-caps-size);
  font-weight: var(--text-label-caps-weight);
  letter-spacing: var(--text-label-caps-ls);
  text-transform: uppercase;
  color: var(--color-on-surface);
  margin-bottom: var(--space-4);
  display: flex;
  align-items: center;
  gap: var(--space-2);
}
.anim-shell {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--gutter);
  background: var(--card-bg);
  border: 1px solid var(--tan-border);
  border-radius: var(--card-radius);
  box-shadow: var(--shadow-card);
  overflow: hidden;
  min-height: 340px;
}
/* Story panel */
.anim-story-panel {
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  padding: var(--space-8);
  border-right: 1px solid var(--tan-border);
  background: var(--color-surface-container-low);
}
.anim-scene-counter {
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--color-outline);
  margin-bottom: var(--space-4);
}
.anim-scene-text {
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.6;
  color: var(--color-on-surface);
  flex: 1;
  display: flex;
  align-items: flex-start;
}
.anim-scene-text p {
  margin: 0;
}
.anim-story-controls {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-top: var(--space-6);
  gap: var(--space-3);
}
/* Canvas panel */
.anim-canvas-panel {
  display: flex;
  align-items: center;
  justify-content: center;
  padding: var(--space-8);
  background: var(--color-surface-container-lowest);
}
.anim-canvas-panel svg {
  width: 100%;
  max-width: 260px;
  height: auto;
}

/* ── Sandbox Simulator ───────────────────────────────────── */
.sandbox-simulator {
  background: var(--card-bg);
  border: 1px solid var(--tan-border);
  border-radius: var(--card-radius);
  box-shadow: var(--shadow-card);
  padding: var(--space-8);
  margin-bottom: var(--space-8);
}
.sim-controls {
  display: flex;
  gap: var(--space-3);
  margin-bottom: var(--space-4);
}
.sim-controls input {
  flex: 1;
  height: 44px;
  padding: 0 var(--space-4);
  font-family: var(--font-mono);
  font-size: var(--text-label-md-size);
  border: 1px solid var(--tan-border);
  border-radius: var(--radius-md);
  background: var(--color-surface-container-lowest);
  color: var(--color-on-surface);
  transition: border-color 0.15s ease;
}
.sim-controls input:focus {
  border-color: var(--color-primary);
  outline: none;
}
.sim-controls input::placeholder { color: var(--color-outline-variant); }
.sim-pop-btn {
  width: 100%;
  height: 44px;
  font-family: var(--font-mono);
  font-size: var(--text-label-md-size);
  font-weight: var(--text-label-md-weight);
  letter-spacing: var(--text-label-md-ls);
  text-transform: uppercase;
  color: var(--color-primary);
  background: transparent;
  border: 1px solid var(--color-primary);
  border-radius: var(--radius-md);
  transition: background 0.15s ease;
  cursor: pointer;
  margin-top: var(--space-3);
}
.sim-pop-btn:hover { background: var(--color-primary-fixed); }

.memory-matrix {
  display: flex;
  flex-direction: column-reverse;
  gap: var(--space-3);
  max-width: 260px;
  margin: var(--space-8) auto 0;
  position: relative;
}
.memory-matrix-label {
  text-align: center;
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--color-secondary);
  opacity: 0.5;
  margin-bottom: var(--space-2);
}
.sim-message {
  margin-top: var(--space-3);
  padding: var(--space-2) var(--space-4);
  background: var(--color-error-container);
  color: var(--color-on-error-container);
  border-radius: var(--radius-md);
  font-family: var(--font-mono);
  font-size: 13px;
  text-align: center;
  display: none;
  animation: fadeIn 0.2s ease;
}
@keyframes fadeIn { from { opacity: 0; } to { opacity: 1; } }
.sim-message.visible { display: block; }

/* ── PYQ Section ─────────────────────────────────────────── */
.pyq-section {
  margin-bottom: var(--space-8);
}
.pyq-card {
  background: var(--card-bg);
  border: 1px solid var(--tan-border);
  border-radius: var(--card-radius);
  padding: var(--space-6);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-6);
  flex-wrap: wrap;
}
.pyq-tag {
  font-family: var(--font-mono);
  font-size: 12px;
  font-weight: 700;
  color: var(--color-primary);
  letter-spacing: 0.08em;
  text-transform: uppercase;
  margin-bottom: var(--space-1);
  display: block;
}
.pyq-question {
  font-family: var(--font-sans);
  font-size: var(--text-body-md-size);
  color: var(--color-on-surface);
  line-height: 1.6;
}
.pyq-question code {
  font-family: var(--font-mono);
  color: var(--color-primary);
}

/* ── Section / Content Headings (inner pages) ────────────── */
.section-title {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  margin-bottom: var(--space-6);
}
.section-title h3 {
  font-family: var(--font-mono);
  font-size: var(--text-headline-sm-size);
  font-weight: var(--text-headline-sm-weight);
  letter-spacing: -0.01em;
  text-transform: uppercase;
}
.underline-accent {
  width: 40px;
  height: 3px;
  background: var(--color-primary);
  border-radius: 2px;
  margin-top: 4px;
}

/* ── Theory Page specifics ───────────────────────────────── */
.theory-header {
  margin-bottom: var(--space-16);
}
.module-eyebrow {
  font-family: var(--font-mono);
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.2em;
  text-transform: uppercase;
  color: var(--color-primary);
  margin-bottom: var(--space-4);
  display: block;
}
.theory-page-title {
  font-family: var(--font-mono);
  font-size: 42px;
  font-weight: 600;
  line-height: 1.1;
  letter-spacing: -0.02em;
  color: var(--color-on-background);
  margin-bottom: var(--space-6);
}
@media (max-width: 768px) {
  .theory-page-title { font-size: 28px; }
}
.theory-intro {
  font-family: var(--font-sans);
  font-size: var(--text-body-lg-size);
  line-height: var(--text-body-lg-lh);
  color: var(--color-on-surface-variant);
  max-width: 72ch;
}
.highlight-term {
  font-family: var(--font-mono);
  font-size: var(--text-label-md-size);
  font-weight: var(--text-label-md-weight);
  color: var(--color-primary);
  background: rgba(255, 219, 203, 0.4);
  padding: 2px 5px;
  border-radius: 3px;
}

/* Complexity panel */
.complexity-panel {
  background: var(--color-primary);
  color: var(--color-on-primary);
  border-radius: var(--card-radius);
  padding: var(--space-8);
  display: flex;
  flex-direction: column;
  justify-content: center;
}
.complexity-panel h3 {
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.2em;
  text-transform: uppercase;
  margin-bottom: var(--space-6);
  padding-bottom: var(--space-3);
  border-bottom: 1px solid rgba(255,255,255,0.2);
}
.complexity-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: var(--space-3) 0;
}
.complexity-row + .complexity-row {
  border-top: 1px solid rgba(255,255,255,0.1);
}
.complexity-op  { font-family: var(--font-sans); font-size: 15px; }
.complexity-val {
  font-family: var(--font-mono);
  font-size: 18px;
  font-weight: 600;
}

/* Primitive ops cards */
.ops-card {
  background: var(--card-bg);
  border: 1px solid var(--tan-border);
  border-top: 4px solid var(--color-primary);
  border-radius: var(--card-radius);
  padding: var(--space-6);
  box-shadow: var(--shadow-card);
  transition: box-shadow 0.2s ease, transform 0.2s ease;
}
.ops-card:hover {
  box-shadow: var(--shadow-elevated);
  transform: translateY(-2px);
}
.ops-card-fn {
  font-family: var(--font-mono);
  font-size: var(--text-label-md-size);
  font-weight: 700;
  color: var(--color-primary);
  margin-bottom: var(--space-2);
  display: block;
}
.ops-card-desc {
  font-family: var(--font-sans);
  font-size: var(--text-body-sm-size);
  line-height: var(--text-body-sm-lh);
  color: var(--color-on-surface-variant);
}

/* Implementation callout box */
.impl-callout {
  background: rgba(239, 225, 198, 0.3);
  border-radius: var(--radius-md);
  padding: var(--space-4);
  font-family: var(--font-mono);
  font-size: var(--text-label-sm-size);
  color: var(--color-on-surface-variant);
  margin-top: var(--space-6);
  line-height: 1.6;
}

/* Modern apps column item */
.app-item {
  padding: var(--space-6);
  border-left: 3px solid var(--color-primary);
}
.app-item-num {
  font-family: var(--font-mono);
  font-size: var(--text-label-md-size);
  font-weight: 700;
  color: var(--color-primary);
  letter-spacing: 0.05em;
  display: block;
  margin-bottom: var(--space-2);
}
.app-item-desc {
  font-family: var(--font-sans);
  font-size: var(--text-body-sm-size);
  color: var(--color-on-surface-variant);
  line-height: 1.6;
}

/* ── Terracotta Bullet ────────────────────────────────────── */
.terracotta-bullet {
  display: inline-block;
  width: 8px;
  height: 8px;
  background: var(--color-primary);
  flex-shrink: 0;
  margin-right: var(--space-3);
  margin-top: 6px;
}

/* ── Footer ──────────────────────────────────────────────── */
.site-footer {
  background: var(--color-surface-container-highest);
  border-top: 1px solid var(--tan-border);
}
.footer-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: var(--gutter);
  padding: var(--space-16) var(--margin-desktop);
  max-width: 1400px;
  margin: 0 auto;
}
.footer-logo {
  font-family: var(--font-mono);
  font-size: 24px;
  font-weight: 600;
  color: var(--color-primary);
  margin-bottom: var(--space-4);
  display: block;
}
.footer-tagline {
  font-family: var(--font-sans);
  font-size: var(--text-body-md-size);
  color: var(--color-on-surface-variant);
  line-height: 1.6;
}
.footer-col-title {
  font-family: var(--font-mono);
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--color-on-surface);
  margin-bottom: var(--space-4);
}
.footer-links {
  display: flex;
  flex-direction: column;
  gap: var(--space-3);
}
.footer-links a {
  font-family: var(--font-sans);
  font-size: var(--text-body-md-size);
  color: var(--color-on-surface-variant);
  text-decoration: none;
  transition: color 0.15s ease;
}
.footer-links a:hover { color: var(--color-primary); }
.footer-bottom {
  padding: var(--space-6) var(--margin-desktop);
  border-top: 1px solid rgba(220, 193, 181, 0.3);
  text-align: center;
  font-family: var(--font-sans);
  font-size: var(--text-body-sm-size);
  color: var(--color-on-surface-variant);
  opacity: 0.7;
}

/* ── Responsive Breakpoints ──────────────────────────────── */
@media (max-width: 1024px) {
  .text-display-lg { font-size: 48px; }
  .footer-grid { grid-template-columns: repeat(2, 1fr); padding: var(--space-12) var(--margin-desktop); }
}

@media (max-width: 900px) {
  /* Interactive animation stacks vertically */
  .anim-shell {
    grid-template-columns: 1fr;
  }
  .anim-story-panel {
    border-right: none;
    border-bottom: 1px solid var(--tan-border);
  }
}

@media (max-width: 768px) {
  .top-nav {
    padding: 0 var(--margin-mobile);
  }
  .top-nav__links,
  .top-nav__search { display: none; }
  .nav-hamburger { display: flex; }

  .app-header { padding: 0 var(--space-4); }
  .app-header__breadcrumb { display: none; }
  .tab-bar { gap: var(--space-4); }

  .sidebar {
    position: fixed;
    top: 64px;
    left: -100%;
    z-index: 95;
    width: 260px;
    height: calc(100vh - 64px);
    transition: left 0.3s ease;
    box-shadow: var(--shadow-lg);
  }
  .sidebar.open { left: 0; }
  .sidebar-toggle { display: flex; }

  .main-content { padding: var(--space-4); }

  .text-display-lg { font-size: 36px; }
  .theory-page-title { font-size: 26px; }

  .footer-grid {
    grid-template-columns: 1fr 1fr;
    padding: var(--space-10) var(--margin-mobile);
  }
}

@media (max-width: 480px) {
  .footer-grid { grid-template-columns: 1fr; }
  .pyq-card { flex-direction: column; align-items: flex-start; }
  .sim-controls { flex-direction: column; }
  .sim-controls input { width: 100%; }
  .anim-story-controls { flex-wrap: wrap; }
}

/* ── Scoped Image Shimmer Effect ── */
.img-shimmer-container {
  position: relative;
  overflow: hidden;
  background-color: var(--color-surface-container); /* Surface token */
  background-image: linear-gradient(
    120deg,
    var(--color-surface-container) 30%,
    var(--color-outline-variant) 45%,
    var(--color-surface-bright) 50%,
    var(--color-outline-variant) 55%,
    var(--color-surface-container) 70%
  );
  background-size: 200% 100%;
  background-position: 200% 0;
  animation: imgShimmerAnim 1.4s ease-in-out infinite;
}

@keyframes imgShimmerAnim {
  0% {
    background-position: 150% 0;
  }
  100% {
    background-position: -150% 0;
  }
}

.shimmer-img {
  opacity: 0;
  width: 100%;
  height: 100%;
  object-fit: contain;
  transition: opacity 0.3s ease-in-out;
  display: block;
}

/* On load: fade image in and hide background shimmer */
.shimmer-img.loaded {
  opacity: 1;
}

/* Fallback state on error */
.shimmer-img.error {
  display: none !important;
}

.img-shimmer-container:has(.error) {
  animation: none !important;
  background: var(--color-surface-container) !important; /* Plain neutral background */
}

/* Respect user's motion preferences */
@media (prefers-reduced-motion: reduce) {
  .img-shimmer-container {
    animation: none !important;
    background: var(--color-surface-container) !important; /* Static neutral background */
  }
}