/* Modern Cyber-Engineering Theme - 4-Bit ALU Interactive Lab */
:root {
  --bg-main: #070a13;
  --bg-card: #0d1322;
  --bg-card-hover: #121a2f;
  --bg-input: #151e36;
  --border-subtle: rgba(255, 255, 255, 0.08);
  --border-active: rgba(0, 240, 255, 0.4);

  --color-primary: #00f0ff;      /* Electric Cyan */
  --color-primary-dim: #00a3ad;
  --color-primary-glow: rgba(0, 240, 255, 0.25);

  --color-arithmetic: #ffb703;   /* Golden Amber for Arithmetic */
  --color-arith-glow: rgba(255, 183, 3, 0.25);

  --color-logic: #a855f7;        /* Violet for Logic Unit */
  --color-logic-glow: rgba(168, 85, 247, 0.25);

  --color-success: #10b981;      /* Emerald Green */
  --color-danger: #ef4444;       /* Crimson Red */
  --color-warning: #f59e0b;

  --signal-high: #00f0ff;
  --signal-high-glow: 0 0 12px rgba(0, 240, 255, 0.7);
  --signal-low: #243049;
  --signal-low-badge: #1a2337;

  --text-main: #f1f5f9;
  --text-muted: #94a3b8;
  --text-dim: #64748b;

  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', monospace;
  --font-display: 'Space Grotesk', var(--font-sans);

  --shadow-card: 0 8px 30px rgba(0, 0, 0, 0.45);
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-xl: 22px;
}

*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  scroll-behavior: smooth;
  font-size: 16px;
}

body {
  background-color: var(--bg-main);
  color: var(--text-main);
  font-family: var(--font-sans);
  line-height: 1.65;
  overflow-x: hidden;
  background-image: 
    radial-gradient(circle at 15% 15%, rgba(0, 240, 255, 0.05) 0%, transparent 40%),
    radial-gradient(circle at 85% 65%, rgba(168, 85, 247, 0.04) 0%, transparent 40%),
    radial-gradient(circle at 50% 90%, rgba(255, 183, 3, 0.04) 0%, transparent 45%);
  background-attachment: fixed;
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-display);
  font-weight: 700;
  color: #fff;
  letter-spacing: -0.02em;
  line-height: 1.25;
}

h1 { font-size: 2.5rem; }
h2 { font-size: 1.85rem; margin-bottom: 0.75rem; }
h3 { font-size: 1.35rem; margin-bottom: 0.5rem; }
h4 { font-size: 1.1rem; }

p {
  color: var(--text-muted);
  margin-bottom: 1.1rem;
}

strong {
  color: var(--text-main);
}

code, kbd, pre {
  font-family: var(--font-mono);
}

.code-inline {
  background: rgba(255, 255, 255, 0.08);
  padding: 2px 6px;
  border-radius: 4px;
  font-size: 0.88em;
  color: var(--color-primary);
  border: 1px solid rgba(255, 255, 255, 0.05);
}

/* App Container */
.app-container {
  max-width: 1240px;
  margin: 0 auto;
  padding: 0 1.5rem 5rem;
}

/* Sticky Top Navigation */
.top-nav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(7, 10, 19, 0.85);
  backdrop-filter: blur(14px);
  -webkit-backdrop-filter: blur(14px);
  border-bottom: 1px solid var(--border-subtle);
  padding: 0.75rem 1.5rem;
  margin-bottom: 2rem;
}

.nav-content {
  max-width: 1240px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
}

.logo-badge {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  text-decoration: none;
  color: #fff;
  font-weight: 700;
  font-family: var(--font-display);
  font-size: 1.15rem;
}

.logo-chip {
  background: linear-gradient(135deg, var(--color-primary), var(--color-logic));
  color: #000;
  font-family: var(--font-mono);
  font-weight: 900;
  font-size: 0.75rem;
  padding: 3px 7px;
  border-radius: 6px;
  letter-spacing: 1px;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  list-style: none;
}

.nav-link {
  color: var(--text-muted);
  text-decoration: none;
  font-size: 0.85rem;
  font-weight: 500;
  padding: 6px 12px;
  border-radius: var(--radius-sm);
  transition: all 0.2s ease;
}

.nav-link:hover, .nav-link.active {
  color: #fff;
  background: rgba(255, 255, 255, 0.06);
}

.nav-controls {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.audio-toggle-btn {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  color: var(--text-muted);
  padding: 6px 12px;
  border-radius: var(--radius-sm);
  font-size: 0.82rem;
  display: flex;
  align-items: center;
  gap: 0.4rem;
  cursor: pointer;
  transition: all 0.2s;
}

.audio-toggle-btn.unmuted {
  border-color: var(--color-primary);
  color: var(--color-primary);
  box-shadow: 0 0 10px var(--color-primary-glow);
}

/* Hero Section */
.hero {
  text-align: center;
  padding: 3.5rem 1rem 2.5rem;
  position: relative;
}

.hero-tag {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  background: rgba(0, 240, 255, 0.1);
  border: 1px solid rgba(0, 240, 255, 0.3);
  color: var(--color-primary);
  font-family: var(--font-mono);
  font-size: 0.8rem;
  font-weight: 600;
  padding: 4px 14px;
  border-radius: 999px;
  margin-bottom: 1.25rem;
  letter-spacing: 0.5px;
  text-transform: uppercase;
}

.hero h1 {
  font-size: 3rem;
  background: linear-gradient(135deg, #ffffff 30%, #94a3b8 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  margin-bottom: 1rem;
}

.hero p.lead {
  font-size: 1.15rem;
  color: var(--text-muted);
  max-width: 780px;
  margin: 0 auto 2rem;
  line-height: 1.7;
}

/* Quick jump pill row */
.quick-pills {
  display: flex;
  justify-content: center;
  flex-wrap: wrap;
  gap: 0.6rem;
  margin-bottom: 2rem;
}

.quick-pill-btn {
  background: rgba(255, 255, 255, 0.04);
  border: 1px solid var(--border-subtle);
  color: var(--text-muted);
  padding: 6px 14px;
  border-radius: 999px;
  font-size: 0.85rem;
  text-decoration: none;
  transition: all 0.2s;
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
}

.quick-pill-btn:hover {
  background: rgba(0, 240, 255, 0.1);
  color: #fff;
  border-color: var(--color-primary);
  transform: translateY(-1px);
}

/* Section Structure */
.content-section {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 2.25rem;
  margin-bottom: 2.5rem;
  box-shadow: var(--shadow-card);
  position: relative;
  overflow: hidden;
}

.content-section::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 2px;
  background: linear-gradient(90deg, transparent, var(--color-primary), transparent);
  opacity: 0.4;
}

.section-header {
  margin-bottom: 1.75rem;
}

.section-num {
  font-family: var(--font-mono);
  font-size: 0.85rem;
  color: var(--color-primary);
  font-weight: 700;
  letter-spacing: 1px;
  text-transform: uppercase;
  margin-bottom: 0.3rem;
  display: block;
}

/* Two-column layout */
.grid-2col {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1.75rem;
  align-items: start;
}

@media (max-width: 960px) {
  .grid-2col {
    grid-template-columns: 1fr;
  }
  .nav-links {
    display: none;
  }
  .hero h1 {
    font-size: 2.2rem;
  }
}

/* Callout alert cards */
.info-callout {
  background: rgba(0, 240, 255, 0.05);
  border-left: 3px solid var(--color-primary);
  padding: 1rem 1.25rem;
  border-radius: 0 var(--radius-md) var(--radius-md) 0;
  margin: 1.25rem 0;
}

.info-callout.amber {
  background: rgba(255, 183, 3, 0.06);
  border-left-color: var(--color-arithmetic);
}

.info-callout.purple {
  background: rgba(168, 85, 247, 0.06);
  border-left-color: var(--color-logic);
}

.info-callout h4 {
  color: #fff;
  margin-bottom: 0.35rem;
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

.info-callout p {
  margin-bottom: 0;
  font-size: 0.92rem;
}

/* Footer */
footer {
  border-top: 1px solid var(--border-subtle);
  padding: 3rem 0;
  text-align: center;
  color: var(--text-dim);
  font-size: 0.9rem;
}