/* ==========================================================================
   Psifiaka Lab - Design System
   Παιχνιδιάρικο, μοντέρνο, εκπαιδευτικό στυλ για Γ' Λυκείου
   ========================================================================== */

/* Custom Fonts - Distinctive picks for educational/playful feel */
@import url('https://fonts.googleapis.com/css2?family=Bricolage+Grotesque:opsz,wght@12..96,400;12..96,600;12..96,800&family=Manrope:wght@400;500;600;700&family=JetBrains+Mono:wght@400;600&display=swap');

/* ---------- CSS Variables ---------- */
:root {
  /* Brand colors - "circuit board" inspired */
  --c-bg: #fdfaf3;
  --c-bg-soft: #f5efe0;
  --c-ink: #1a1d2e;
  --c-ink-soft: #4a4e6a;
  --c-muted: #8b8fa8;
  
  /* Accent palette - vivid but not garish */
  --c-primary: #ff5c39;        /* energetic orange */
  --c-secondary: #2563eb;      /* electric blue */
  --c-tertiary: #16a34a;       /* logic green */
  --c-quaternary: #f59e0b;     /* signal yellow */
  --c-purple: #8b5cf6;         /* digital purple */
  
  /* Semantic */
  --c-high: #16a34a;           /* logic 1 / HIGH */
  --c-low:  #ef4444;           /* logic 0 / LOW */
  --c-clock: #2563eb;
  
  /* Surfaces */
  --c-card: #ffffff;
  --c-border: #1a1d2e;
  --c-shadow: rgba(26, 29, 46, 0.12);
  
  /* Spacing scale */
  --s-1: 0.25rem;
  --s-2: 0.5rem;
  --s-3: 0.75rem;
  --s-4: 1rem;
  --s-5: 1.5rem;
  --s-6: 2rem;
  --s-7: 3rem;
  --s-8: 4rem;
  --s-9: 6rem;
  
  /* Radius */
  --r-sm: 8px;
  --r-md: 16px;
  --r-lg: 24px;
  --r-xl: 32px;
  
  /* Typography */
  --f-display: 'Bricolage Grotesque', Georgia, serif;
  --f-body: 'Manrope', system-ui, sans-serif;
  --f-mono: 'JetBrains Mono', ui-monospace, monospace;
  
  /* Layout */
  --container-max: 1200px;
  --content-max: 760px;
  --sidebar-w: 260px;
}

/* Dark mode */
@media (prefers-color-scheme: dark) {
  :root {
    --c-bg: #0f1117;
    --c-bg-soft: #161922;
    --c-ink: #f5efe0;
    --c-ink-soft: #c5c8d6;
    --c-muted: #6b7088;
    --c-card: #1a1d2e;
    --c-border: #f5efe0;
    --c-shadow: rgba(0, 0, 0, 0.4);
  }
}

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

html {
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--f-body);
  font-size: 17px;
  line-height: 1.65;
  color: var(--c-ink);
  background: var(--c-bg);
  background-image: 
    radial-gradient(circle at 25% 10%, rgba(255, 92, 57, 0.06) 0%, transparent 40%),
    radial-gradient(circle at 75% 80%, rgba(37, 99, 235, 0.06) 0%, transparent 40%);
  min-height: 100vh;
  overflow-x: hidden;
}

/* Subtle grid pattern background */
body::before {
  content: '';
  position: fixed;
  inset: 0;
  background-image: 
    linear-gradient(rgba(26, 29, 46, 0.03) 1px, transparent 1px),
    linear-gradient(90deg, rgba(26, 29, 46, 0.03) 1px, transparent 1px);
  background-size: 40px 40px;
  pointer-events: none;
  z-index: -1;
}

img, svg { max-width: 100%; display: block; }
a { color: var(--c-secondary); text-decoration: none; transition: color 0.2s; }
a:hover { color: var(--c-primary); }

/* ---------- Typography ---------- */
h1, h2, h3, h4 {
  font-family: var(--f-display);
  font-weight: 800;
  line-height: 1.1;
  color: var(--c-ink);
  letter-spacing: -0.02em;
}

h1 { font-size: clamp(2.2rem, 5vw, 4rem); }
h2 { font-size: clamp(1.6rem, 3.5vw, 2.4rem); margin-top: var(--s-7); margin-bottom: var(--s-4); }
h3 { font-size: clamp(1.2rem, 2.5vw, 1.5rem); margin-top: var(--s-5); margin-bottom: var(--s-3); }
h4 { font-size: 1.1rem; margin-top: var(--s-4); margin-bottom: var(--s-2); }

p { margin-bottom: var(--s-4); }
strong { font-weight: 700; color: var(--c-ink); }
code {
  font-family: var(--f-mono);
  font-size: 0.92em;
  background: var(--c-bg-soft);
  padding: 2px 6px;
  border-radius: 4px;
  border: 1px solid var(--c-shadow);
}

/* ---------- Layout helpers ---------- */
.container {
  max-width: var(--container-max);
  margin: 0 auto;
  padding: 0 var(--s-5);
}

.content-wrap {
  max-width: var(--content-max);
  margin: 0 auto;
}

/* ==========================================================================
   NAVIGATION HEADER
   ========================================================================== */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(253, 250, 243, 0.85);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 2px solid var(--c-ink);
}
@media (prefers-color-scheme: dark) {
  .site-header { background: rgba(15, 17, 23, 0.85); }
}

.nav-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--s-4) var(--s-5);
  max-width: var(--container-max);
  margin: 0 auto;
}

.logo {
  display: flex;
  align-items: center;
  gap: var(--s-3);
  font-family: var(--f-display);
  font-weight: 800;
  font-size: 1.4rem;
  color: var(--c-ink);
  letter-spacing: -0.02em;
}
.logo:hover { color: var(--c-ink); }

.logo-mark {
  width: 38px;
  height: 38px;
  background: var(--c-primary);
  border: 2px solid var(--c-ink);
  border-radius: 10px;
  display: grid;
  place-items: center;
  font-family: var(--f-mono);
  font-weight: 600;
  color: var(--c-ink);
  font-size: 1rem;
  box-shadow: 3px 3px 0 var(--c-ink);
  transform: rotate(-3deg);
  transition: transform 0.2s ease;
}
.logo:hover .logo-mark { transform: rotate(3deg) scale(1.05); }

.nav-toggle {
  display: none;
  background: transparent;
  border: 2px solid var(--c-ink);
  border-radius: var(--r-sm);
  padding: var(--s-2) var(--s-3);
  cursor: pointer;
  font-family: var(--f-body);
  font-weight: 600;
  color: var(--c-ink);
}

.nav-list {
  list-style: none;
  display: flex;
  gap: var(--s-2);
  align-items: center;
}

.nav-list a {
  font-weight: 600;
  color: var(--c-ink-soft);
  padding: var(--s-2) var(--s-3);
  border-radius: var(--r-sm);
  transition: all 0.15s;
}
.nav-list a:hover, .nav-list a.active {
  color: var(--c-primary);
  background: var(--c-bg-soft);
}

/* Mobile nav */
@media (max-width: 900px) {
  .nav-toggle { display: block; }
  .nav-list {
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    flex-direction: column;
    background: var(--c-bg);
    border-bottom: 2px solid var(--c-ink);
    padding: var(--s-4);
    gap: var(--s-1);
    align-items: stretch;
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.3s ease;
  }
  .nav-list.is-open { max-height: 80vh; overflow-y: auto; }
  .nav-list a { padding: var(--s-3); border-radius: var(--r-sm); }
}

/* ==========================================================================
   HERO (homepage)
   ========================================================================== */
.hero {
  padding: var(--s-9) var(--s-5) var(--s-8);
  position: relative;
  overflow: hidden;
}

.hero-content {
  max-width: var(--container-max);
  margin: 0 auto;
  position: relative;
  z-index: 2;
}

.hero-eyebrow {
  display: inline-block;
  font-family: var(--f-mono);
  font-size: 0.85rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--c-primary);
  background: rgba(255, 92, 57, 0.1);
  padding: var(--s-2) var(--s-3);
  border-radius: 100px;
  margin-bottom: var(--s-5);
  border: 1.5px solid var(--c-primary);
}

.hero h1 {
  margin-bottom: var(--s-4);
  max-width: 18ch;
}

.hero h1 .highlight {
  background: linear-gradient(120deg, var(--c-primary) 0%, var(--c-quaternary) 100%);
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
  position: relative;
  display: inline-block;
}

.hero-lede {
  font-size: clamp(1.05rem, 2vw, 1.25rem);
  color: var(--c-ink-soft);
  max-width: 55ch;
  margin-bottom: var(--s-6);
}

.hero-cta {
  display: inline-flex;
  align-items: center;
  gap: var(--s-3);
  background: var(--c-ink);
  color: var(--c-bg);
  padding: var(--s-4) var(--s-5);
  border-radius: var(--r-md);
  font-weight: 700;
  font-family: var(--f-display);
  font-size: 1.05rem;
  border: 2px solid var(--c-ink);
  box-shadow: 4px 4px 0 var(--c-primary);
  transition: all 0.15s;
}
.hero-cta:hover {
  transform: translate(-2px, -2px);
  box-shadow: 6px 6px 0 var(--c-primary);
  color: var(--c-bg);
}
.hero-cta:active {
  transform: translate(0, 0);
  box-shadow: 2px 2px 0 var(--c-primary);
}

/* Decorative floating shapes */
.hero-deco {
  position: absolute;
  z-index: 1;
  pointer-events: none;
}
.hero-deco-1 {
  top: 15%;
  right: 8%;
  width: 80px;
  height: 80px;
  background: var(--c-secondary);
  border: 2px solid var(--c-ink);
  border-radius: 18px;
  transform: rotate(15deg);
  animation: float 6s ease-in-out infinite;
}
.hero-deco-2 {
  top: 55%;
  right: 18%;
  width: 50px;
  height: 50px;
  background: var(--c-quaternary);
  border: 2px solid var(--c-ink);
  border-radius: 50%;
  animation: float 4s ease-in-out infinite reverse;
}
.hero-deco-3 {
  top: 30%;
  right: 25%;
  width: 60px;
  height: 60px;
  background: var(--c-tertiary);
  border: 2px solid var(--c-ink);
  transform: rotate(45deg);
  animation: float 5s ease-in-out infinite 1s;
}

@keyframes float {
  0%, 100% { transform: translateY(0) rotate(15deg); }
  50% { transform: translateY(-20px) rotate(20deg); }
}

@media (max-width: 700px) {
  .hero-deco { display: none; }
}

/* ==========================================================================
   CHAPTER GRID (homepage)
   ========================================================================== */
.chapters-section {
  padding: var(--s-7) var(--s-5);
  max-width: var(--container-max);
  margin: 0 auto;
}

.section-header {
  text-align: center;
  margin-bottom: var(--s-7);
}

.section-header h2 {
  margin-top: 0;
}

.section-header p {
  color: var(--c-ink-soft);
  font-size: 1.1rem;
}

.chapters-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: var(--s-5);
}

.chapter-card {
  background: var(--c-card);
  border: 2px solid var(--c-ink);
  border-radius: var(--r-md);
  padding: var(--s-5);
  position: relative;
  transition: all 0.2s ease;
  box-shadow: 4px 4px 0 var(--c-ink);
  display: block;
  color: var(--c-ink);
  overflow: hidden;
}
.chapter-card:hover {
  transform: translate(-3px, -3px);
  box-shadow: 7px 7px 0 var(--c-ink);
  color: var(--c-ink);
}

.chapter-card .chapter-num {
  font-family: var(--f-mono);
  font-size: 0.85rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--c-muted);
  margin-bottom: var(--s-2);
}

.chapter-card h3 {
  font-size: 1.3rem;
  margin: 0 0 var(--s-3);
}

.chapter-card p {
  color: var(--c-ink-soft);
  font-size: 0.95rem;
  margin: 0;
}

.chapter-card .chapter-icon {
  position: absolute;
  top: var(--s-4);
  right: var(--s-4);
  width: 40px;
  height: 40px;
  border-radius: 10px;
  display: grid;
  place-items: center;
  font-size: 1.2rem;
  border: 2px solid var(--c-ink);
}

/* Color variants for chapters */
.chapter-card[data-num="1"] .chapter-icon { background: #ffe4d6; }
.chapter-card[data-num="2"] .chapter-icon { background: #d6e4ff; }
.chapter-card[data-num="3"] .chapter-icon { background: #d6ffe4; }
.chapter-card[data-num="4"] .chapter-icon { background: #ffe4f5; }
.chapter-card[data-num="5"] .chapter-icon { background: #fff4d6; }
.chapter-card[data-num="6"] .chapter-icon { background: #e4d6ff; }
.chapter-card[data-num="7"] .chapter-icon { background: #d6fff4; }
.chapter-card[data-num="8"] .chapter-icon { background: #ffd6d6; }
.chapter-card[data-num="9"] .chapter-icon { background: #d6e4ff; }
.chapter-card[data-num="10"] .chapter-icon { background: #f5d6ff; }

/* ==========================================================================
   CHAPTER PAGE LAYOUT
   ========================================================================== */
.chapter-layout {
  display: grid;
  grid-template-columns: var(--sidebar-w) 1fr;
  gap: var(--s-7);
  max-width: var(--container-max);
  margin: 0 auto;
  padding: var(--s-6) var(--s-5);
}

.chapter-sidebar {
  position: sticky;
  top: 90px;
  height: fit-content;
  max-height: calc(100vh - 110px);
  overflow-y: auto;
  padding-right: var(--s-3);
}

.chapter-sidebar h4 {
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--c-muted);
  margin-top: var(--s-4);
  margin-bottom: var(--s-2);
}

.chapter-sidebar ul {
  list-style: none;
  padding: 0;
}

.chapter-sidebar li {
  margin-bottom: var(--s-1);
}

.chapter-sidebar a {
  display: block;
  padding: var(--s-2) var(--s-3);
  border-radius: var(--r-sm);
  color: var(--c-ink-soft);
  font-size: 0.92rem;
  font-weight: 500;
  border-left: 3px solid transparent;
}
.chapter-sidebar a:hover {
  background: var(--c-bg-soft);
  color: var(--c-ink);
}
.chapter-sidebar a.active {
  background: var(--c-bg-soft);
  color: var(--c-primary);
  border-left-color: var(--c-primary);
  font-weight: 600;
}

.chapter-content {
  min-width: 0;
}

@media (max-width: 900px) {
  .chapter-layout {
    grid-template-columns: 1fr;
  }
  .chapter-sidebar {
    position: static;
    max-height: none;
    border-bottom: 2px solid var(--c-ink);
    padding-bottom: var(--s-5);
    margin-bottom: var(--s-5);
  }
}

/* Chapter header */
.chapter-hero {
  padding: var(--s-5) 0 var(--s-6);
  border-bottom: 2px dashed var(--c-shadow);
  margin-bottom: var(--s-6);
}

.chapter-hero .chapter-num {
  display: inline-block;
  font-family: var(--f-mono);
  font-size: 0.85rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--c-bg);
  background: var(--c-primary);
  padding: var(--s-1) var(--s-3);
  border-radius: 100px;
  margin-bottom: var(--s-3);
  border: 1.5px solid var(--c-ink);
}

.chapter-hero h1 {
  font-size: clamp(1.8rem, 4vw, 3rem);
  margin: 0 0 var(--s-3);
}

.chapter-hero .lede {
  font-size: 1.15rem;
  color: var(--c-ink-soft);
  max-width: 65ch;
}

/* Section dividers */
.section-divider {
  display: flex;
  align-items: center;
  gap: var(--s-3);
  margin: var(--s-7) 0 var(--s-5);
  padding-top: var(--s-3);
}
.section-divider::after {
  content: '';
  flex: 1;
  height: 2px;
  background: var(--c-ink);
  opacity: 0.15;
}
.section-divider .badge {
  font-family: var(--f-mono);
  font-size: 0.8rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  background: var(--c-ink);
  color: var(--c-bg);
  padding: var(--s-1) var(--s-3);
  border-radius: var(--r-sm);
}

/* Info callouts */
.callout {
  background: var(--c-card);
  border: 2px solid var(--c-ink);
  border-radius: var(--r-md);
  padding: var(--s-5);
  margin: var(--s-5) 0;
  box-shadow: 3px 3px 0 var(--c-ink);
  position: relative;
}
.callout-title {
  font-family: var(--f-display);
  font-weight: 700;
  font-size: 1.1rem;
  margin-bottom: var(--s-2);
  display: flex;
  align-items: center;
  gap: var(--s-2);
}
.callout--info { background: linear-gradient(135deg, #d6e4ff 0%, #fff 100%); }
.callout--tip { background: linear-gradient(135deg, #d6ffe4 0%, #fff 100%); }
.callout--warning { background: linear-gradient(135deg, #fff4d6 0%, #fff 100%); }
@media (prefers-color-scheme: dark) {
  .callout--info { background: linear-gradient(135deg, rgba(37, 99, 235, 0.2) 0%, var(--c-card) 100%); }
  .callout--tip { background: linear-gradient(135deg, rgba(22, 163, 74, 0.2) 0%, var(--c-card) 100%); }
  .callout--warning { background: linear-gradient(135deg, rgba(245, 158, 11, 0.2) 0%, var(--c-card) 100%); }
}

/* Tables */
table {
  border-collapse: collapse;
  width: 100%;
  margin: var(--s-5) 0;
  background: var(--c-card);
  border: 2px solid var(--c-ink);
  border-radius: var(--r-md);
  overflow: hidden;
  font-family: var(--f-mono);
}
th, td {
  padding: var(--s-3) var(--s-4);
  text-align: center;
  border-bottom: 1px solid var(--c-shadow);
}
th {
  background: var(--c-ink);
  color: var(--c-bg);
  font-family: var(--f-display);
  font-weight: 700;
  font-size: 0.95rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}
tr:last-child td { border-bottom: none; }
tr:hover td { background: var(--c-bg-soft); }

/* Lists */
.chapter-content ul, .chapter-content ol {
  margin: var(--s-4) 0;
  padding-left: var(--s-5);
}
.chapter-content li {
  margin-bottom: var(--s-2);
}

/* PDF embed */
.pdf-embed-wrap {
  border: 2px solid var(--c-ink);
  border-radius: var(--r-md);
  overflow: hidden;
  box-shadow: 4px 4px 0 var(--c-ink);
  background: var(--c-card);
  margin: var(--s-5) 0;
}
.pdf-embed-wrap iframe {
  width: 100%;
  height: 600px;
  border: 0;
  display: block;
}
.pdf-embed-tabs {
  display: flex;
  border-bottom: 2px solid var(--c-ink);
}
.pdf-tab-btn {
  flex: 1;
  padding: var(--s-3) var(--s-4);
  background: var(--c-bg-soft);
  border: none;
  border-right: 2px solid var(--c-ink);
  font-family: var(--f-display);
  font-weight: 700;
  font-size: 0.95rem;
  cursor: pointer;
  color: var(--c-ink-soft);
  transition: all 0.15s;
}
.pdf-tab-btn:last-child { border-right: none; }
.pdf-tab-btn.active {
  background: var(--c-primary);
  color: var(--c-bg);
}
.pdf-tab-btn:hover:not(.active) { background: var(--c-bg); color: var(--c-ink); }

.pdf-download-link {
  display: inline-flex;
  align-items: center;
  gap: var(--s-2);
  padding: var(--s-2) var(--s-4);
  font-family: var(--f-display);
  font-weight: 600;
  font-size: 0.9rem;
  background: var(--c-bg-soft);
  border-radius: var(--r-sm);
  margin: var(--s-2);
}

/* ==========================================================================
   INTERACTIVE WIDGETS
   ========================================================================== */
.interactive {
  background: var(--c-card);
  border: 2px solid var(--c-ink);
  border-radius: var(--r-lg);
  padding: var(--s-6);
  margin: var(--s-5) 0;
  box-shadow: 5px 5px 0 var(--c-ink);
  position: relative;
}

.interactive-label {
  position: absolute;
  top: -12px;
  left: var(--s-5);
  background: var(--c-primary);
  color: var(--c-bg);
  font-family: var(--f-mono);
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  padding: 4px 12px;
  border-radius: 100px;
  border: 2px solid var(--c-ink);
}

.interactive h3 {
  margin-top: var(--s-2);
}

.interactive-explainer {
  color: var(--c-ink-soft);
  font-size: 0.95rem;
  margin-bottom: var(--s-5);
}

/* Toggle button (digital input) */
.bit-toggle {
  display: inline-flex;
  flex-direction: column;
  align-items: center;
  gap: var(--s-2);
  cursor: pointer;
  user-select: none;
}
.bit-toggle-label {
  font-family: var(--f-display);
  font-weight: 700;
  font-size: 1.2rem;
  color: var(--c-ink);
}
.bit-btn {
  width: 70px;
  height: 70px;
  border-radius: 50%;
  border: 3px solid var(--c-ink);
  background: var(--c-low);
  color: white;
  font-family: var(--f-mono);
  font-size: 1.8rem;
  font-weight: 700;
  cursor: pointer;
  transition: all 0.15s;
  box-shadow: 3px 3px 0 var(--c-ink);
}
.bit-btn:hover {
  transform: translate(-1px, -1px);
  box-shadow: 4px 4px 0 var(--c-ink);
}
.bit-btn:active {
  transform: translate(1px, 1px);
  box-shadow: 1px 1px 0 var(--c-ink);
}
.bit-btn.is-high {
  background: var(--c-high);
}

/* Output indicator */
.output-led {
  display: inline-flex;
  flex-direction: column;
  align-items: center;
  gap: var(--s-2);
}
.output-led-label {
  font-family: var(--f-display);
  font-weight: 700;
  font-size: 1.2rem;
}
.led {
  width: 70px;
  height: 70px;
  border-radius: 50%;
  border: 3px solid var(--c-ink);
  background: var(--c-low);
  color: white;
  font-family: var(--f-mono);
  font-size: 1.8rem;
  font-weight: 700;
  display: grid;
  place-items: center;
  transition: all 0.3s;
}
.led.is-high {
  background: var(--c-high);
  box-shadow: 0 0 20px rgba(22, 163, 74, 0.5), 3px 3px 0 var(--c-ink);
}
.led.is-low {
  box-shadow: 3px 3px 0 var(--c-ink);
}

/* Generic IO row */
.io-row {
  display: flex;
  flex-wrap: wrap;
  gap: var(--s-6);
  align-items: center;
  justify-content: center;
  padding: var(--s-5);
}

/* Flip-flop visual block */
.ff-visual {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--s-5);
  flex-wrap: wrap;
  padding: var(--s-5);
}

.ff-inputs, .ff-outputs {
  display: flex;
  flex-direction: column;
  gap: var(--s-4);
}

.ff-box {
  width: 140px;
  height: 140px;
  border: 3px solid var(--c-ink);
  border-radius: var(--r-md);
  background: var(--c-bg-soft);
  display: grid;
  place-items: center;
  font-family: var(--f-display);
  font-weight: 800;
  font-size: 1.8rem;
  color: var(--c-ink);
  box-shadow: 4px 4px 0 var(--c-ink);
  position: relative;
}

.ff-arrow {
  font-family: var(--f-mono);
  color: var(--c-muted);
  font-size: 1.5rem;
}

/* Truth table highlight */
.truth-table tr.is-active td {
  background: rgba(255, 92, 57, 0.15);
  font-weight: 700;
  position: relative;
}
.truth-table tr.is-active td:first-child::before {
  content: '▶';
  position: absolute;
  left: 4px;
  color: var(--c-primary);
}

/* Clock control */
.clock-controls {
  display: flex;
  flex-wrap: wrap;
  gap: var(--s-3);
  align-items: center;
  justify-content: center;
  padding: var(--s-4);
  background: var(--c-bg-soft);
  border: 2px dashed var(--c-ink);
  border-radius: var(--r-md);
  margin-top: var(--s-4);
}

.btn {
  background: var(--c-card);
  color: var(--c-ink);
  border: 2px solid var(--c-ink);
  padding: var(--s-2) var(--s-4);
  border-radius: var(--r-sm);
  font-family: var(--f-display);
  font-weight: 700;
  font-size: 0.95rem;
  cursor: pointer;
  transition: all 0.15s;
  box-shadow: 2px 2px 0 var(--c-ink);
}
.btn:hover {
  transform: translate(-1px, -1px);
  box-shadow: 3px 3px 0 var(--c-ink);
}
.btn:active {
  transform: translate(1px, 1px);
  box-shadow: 1px 1px 0 var(--c-ink);
}
.btn--primary { background: var(--c-primary); color: white; }
.btn--secondary { background: var(--c-secondary); color: white; }

/* Timing diagram canvas */
.timing-canvas-wrap {
  background: var(--c-card);
  border: 2px solid var(--c-ink);
  border-radius: var(--r-md);
  padding: var(--s-3);
  margin-top: var(--s-4);
  overflow-x: auto;
}
.timing-canvas {
  display: block;
  width: 100%;
  min-width: 600px;
  height: 240px;
}

/* ==========================================================================
   PROMO BANNER (homepage only)
   ========================================================================== */
.promo-banner {
  margin: var(--s-7) auto;
  max-width: 1100px;
  padding: 0 var(--s-4);
}
.promo-content {
  background: linear-gradient(135deg, var(--c-primary) 0%, #ff7a4d 100%);
  border: 3px solid var(--c-ink);
  border-radius: 24px;
  padding: var(--s-6);
  box-shadow: 6px 6px 0 var(--c-ink);
  display: grid;
  grid-template-columns: 1.5fr 1fr;
  gap: var(--s-5);
  align-items: center;
  color: white;
  position: relative;
  overflow: hidden;
}
.promo-content::before {
  content: '🎓';
  position: absolute;
  top: -20px;
  right: -10px;
  font-size: 7rem;
  opacity: 0.12;
  transform: rotate(15deg);
}
.promo-eyebrow {
  display: inline-block;
  background: rgba(255,255,255,0.2);
  border: 2px solid rgba(255,255,255,0.4);
  padding: 4px 14px;
  border-radius: 100px;
  font-family: var(--f-mono);
  font-size: 0.78rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  margin-bottom: var(--s-2);
}
.promo-title {
  font-family: var(--f-display);
  font-weight: 800;
  font-size: 1.8rem;
  line-height: 1.2;
  margin-bottom: var(--s-3);
  color: white;
}
.promo-lede {
  font-size: 1rem;
  line-height: 1.6;
  margin: 0;
  opacity: 0.95;
}
.promo-lede strong { color: var(--c-ink); background: rgba(255,255,255,0.6); padding: 0 6px; border-radius: 4px; }
.promo-actions {
  display: flex;
  flex-direction: column;
  gap: var(--s-3);
  align-items: center;
  position: relative;
  z-index: 1;
}
.promo-btn {
  display: inline-block;
  padding: 14px 24px;
  font-family: var(--f-display);
  font-weight: 700;
  font-size: 1rem;
  text-decoration: none;
  border-radius: 100px;
  border: 3px solid var(--c-ink);
  transition: all 0.2s;
  text-align: center;
}
.promo-btn--primary {
  background: var(--c-bg);
  color: var(--c-ink);
  box-shadow: 4px 4px 0 var(--c-ink);
}
.promo-btn--primary:hover {
  transform: translate(-2px, -2px);
  box-shadow: 6px 6px 0 var(--c-ink);
  background: white;
}
.promo-socials {
  display: flex;
  gap: 10px;
  justify-content: center;
}
.promo-socials a {
  display: grid;
  place-items: center;
  width: 44px;
  height: 44px;
  background: rgba(255,255,255,0.2);
  border: 2px solid rgba(255,255,255,0.5);
  border-radius: 50%;
  font-size: 1.2rem;
  text-decoration: none;
  transition: all 0.2s;
}
.promo-socials a:hover {
  background: white;
  border-color: var(--c-ink);
  transform: translateY(-2px) scale(1.1);
}
@media (max-width: 800px) {
  .promo-content {
    grid-template-columns: 1fr;
    text-align: center;
    padding: var(--s-5) var(--s-4);
  }
  .promo-title { font-size: 1.5rem; }
}

/* ==========================================================================
   FOOTER
   ========================================================================== */
.site-footer {
  margin-top: var(--s-9);
  padding: var(--s-7) var(--s-5) var(--s-5);
  background: var(--c-ink);
  color: var(--c-bg);
}
.site-footer .container {
  max-width: 1100px;
  margin: 0 auto;
}
.site-footer p { margin: 0 0 0.5rem; opacity: 0.85; line-height: 1.5; }
.site-footer a { color: var(--c-quaternary); transition: color 0.15s; }
.site-footer a:hover { color: var(--c-primary); }

.footer-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: var(--s-5);
  margin-bottom: var(--s-5);
}

.footer-col {
  display: flex;
  flex-direction: column;
}

.site-footer .footer-mark {
  font-family: var(--f-display);
  font-weight: 800;
  font-size: 1.4rem;
  margin-bottom: var(--s-2);
  color: var(--c-primary);
}

.footer-title {
  font-family: var(--f-display);
  font-weight: 700;
  font-size: 1rem;
  margin-bottom: var(--s-2);
  color: var(--c-bg);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.footer-link {
  display: inline-block;
  margin-top: var(--s-2);
  padding: 6px 14px;
  background: rgba(255,255,255,0.08);
  border-radius: 100px;
  font-size: 0.88rem;
  font-weight: 600;
  text-decoration: none;
  border: 1px solid rgba(255,255,255,0.12);
  transition: all 0.2s;
}
.footer-link:hover {
  background: var(--c-primary);
  border-color: var(--c-primary);
  color: white !important;
  transform: translateY(-1px);
}
.footer-link--cta {
  background: var(--c-primary);
  border-color: var(--c-primary);
  color: white !important;
}
.footer-link--cta:hover {
  background: var(--c-quaternary);
  border-color: var(--c-quaternary);
}

.footer-social {
  list-style: none;
  padding: 0;
  margin: 0;
  display: flex;
  flex-direction: column;
  gap: 6px;
}
.footer-social a {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 6px 4px;
  text-decoration: none;
  font-size: 0.92rem;
  color: var(--c-bg) !important;
  opacity: 0.9;
  transition: opacity 0.15s, transform 0.15s;
}
.footer-social a:hover {
  opacity: 1;
  transform: translateX(3px);
  color: var(--c-quaternary) !important;
}
.social-icon {
  display: inline-grid;
  place-items: center;
  width: 28px;
  height: 28px;
  background: rgba(255,255,255,0.1);
  border-radius: 50%;
  font-size: 0.95rem;
}

.footer-bottom {
  padding-top: var(--s-4);
  border-top: 1px solid rgba(255,255,255,0.1);
  text-align: center;
}
.footer-bottom p {
  opacity: 0.7;
}

@media (max-width: 600px) {
  .footer-grid {
    text-align: center;
    grid-template-columns: 1fr;
  }
  .footer-social {
    align-items: center;
  }
}

/* ==========================================================================
   UTILITY
   ========================================================================== */
.mono { font-family: var(--f-mono); }
.muted { color: var(--c-muted); }
.center { text-align: center; }
.mt-5 { margin-top: var(--s-5); }
.mt-6 { margin-top: var(--s-6); }

/* Reduced motion */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}