/* ===========================================================
   How Computers Actually Work — shared design system
   =========================================================== */

:root {
  --bg: #0a0e14;
  --bg-panel: #121821;
  --bg-panel-2: #17202b;
  --border: #263140;
  --text: #e7edf5;
  --text-dim: #93a2b5;
  --text-faint: #5c6b7f;
  --accent: #38bdf8;       /* cool blue accent */
  --accent-2: #a78bfa;     /* violet accent */
  --accent-glow: rgba(56, 189, 248, 0.55);
  --accent-2-glow: rgba(167, 139, 250, 0.55);
  --on: #ffcc4d;           /* signal = 1 (amber glow) */
  --on-glow: rgba(255, 204, 77, 0.55);
  --off: #3a4656;          /* signal = 0 (dim gray) */
  --good: #34d399;
  --good-glow: rgba(52, 211, 153, 0.55);
  --danger: #f87171;
  --radius: 14px;
  --serif: Georgia, 'Iowan Old Style', 'Times New Roman', serif;
  --sans: -apple-system, BlinkMacSystemFont, 'Segoe UI', Inter, Roboto, Helvetica, Arial, sans-serif;
  --mono: 'SF Mono', 'Consolas', 'Menlo', monospace;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--sans);
  scroll-behavior: smooth;
}

body {
  background-image:
    radial-gradient(circle at 15% 0%, rgba(56,189,248,0.06), transparent 40%),
    radial-gradient(circle at 85% 20%, rgba(167,139,250,0.05), transparent 45%);
  background-attachment: fixed;
  padding-bottom: 80px;
}

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

h1, h2, h3 {
  font-family: var(--sans);
  font-weight: 700;
  letter-spacing: -0.01em;
  line-height: 1.25;
}

h1 { font-size: clamp(2rem, 4vw, 2.8rem); }
h2 { font-size: clamp(1.4rem, 2.5vw, 1.9rem); margin-top: 3rem; }
h3 { font-size: 1.15rem; color: var(--accent); }

p { line-height: 1.7; color: var(--text-dim); font-size: 1.05rem; }
strong { color: var(--text); }

.container {
  max-width: 860px;
  margin: 0 auto;
  padding: 0 24px;
}

/* ---------- Top nav ---------- */
.topnav {
  position: sticky;
  top: 0;
  z-index: 50;
  background: rgba(10, 14, 20, 0.85);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--border);
}

.topnav-inner {
  max-width: 980px;
  margin: 0 auto;
  padding: 14px 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  flex-wrap: wrap;
}

.brand {
  font-weight: 800;
  font-size: 1rem;
  color: var(--text);
  display: flex;
  align-items: center;
  gap: 8px;
}
.brand:hover { text-decoration: none; }
.brand .dot { width: 9px; height: 9px; border-radius: 50%; background: var(--on); box-shadow: 0 0 10px var(--on-glow); }

.steps {
  display: flex;
  gap: 4px;
  flex-wrap: wrap;
}

.step-link {
  font-size: 0.85rem;
  padding: 6px 12px;
  border-radius: 999px;
  color: var(--text-dim);
  border: 1px solid transparent;
  white-space: nowrap;
}
.step-link:hover { text-decoration: none; color: var(--text); border-color: var(--border); }
.step-link.active { color: var(--bg); background: var(--accent); font-weight: 600; }

/* ---------- Hero ---------- */
.hero {
  padding: 64px 0 32px;
  text-align: center;
}
.hero .eyebrow {
  color: var(--accent);
  font-size: 0.85rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  margin-bottom: 12px;
}
.hero p.lead {
  max-width: 600px;
  margin: 16px auto 0;
  font-size: 1.15rem;
}

/* ---------- Cards / grid ---------- */
.grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 16px;
  margin: 32px 0;
}

.card {
  background: var(--bg-panel);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 22px;
  transition: transform 0.15s ease, border-color 0.15s ease;
  display: block;
}
.card:hover { transform: translateY(-2px); border-color: var(--accent); text-decoration: none; }
.card .num {
  display: inline-block;
  font-family: var(--mono);
  font-size: 0.75rem;
  color: var(--bg);
  background: var(--accent);
  padding: 2px 8px;
  border-radius: 6px;
  margin-bottom: 10px;
  font-weight: 700;
}
.card h3 { margin: 0 0 8px; color: var(--text); font-size: 1.1rem; }
.card p { margin: 0; font-size: 0.95rem; }

/* ---------- Panels (interactive demo containers) ---------- */
.panel {
  background: var(--bg-panel);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 28px;
  margin: 28px 0;
}
.panel-label {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--text-faint);
  font-weight: 700;
  margin-bottom: 6px;
}
.panel .caption {
  text-align: center;
  color: var(--text-faint);
  font-size: 0.85rem;
  margin-top: 14px;
}

.demo-stage {
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 20px 0;
}

/* ---------- Toggle switch button ---------- */
.toggle {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  cursor: pointer;
  user-select: none;
  background: none;
  border: none;
  padding: 0;
  font-family: var(--sans);
}

.toggle-track {
  width: 56px;
  height: 30px;
  border-radius: 999px;
  background: var(--off);
  border: 1px solid var(--border);
  position: relative;
  transition: background 0.2s ease, box-shadow 0.2s ease;
  flex-shrink: 0;
}
.toggle-track .knob {
  position: absolute;
  top: 3px; left: 3px;
  width: 22px; height: 22px;
  border-radius: 50%;
  background: #cbd5e1;
  transition: left 0.2s ease, background 0.2s ease;
}
.toggle.on .toggle-track {
  background: var(--on);
  box-shadow: 0 0 16px var(--on-glow);
}
.toggle.on .toggle-track .knob {
  left: 29px;
  background: #1a1200;
}
.toggle.input-a.on .toggle-track { background: var(--accent); box-shadow: 0 0 16px var(--accent-glow); }
.toggle.input-b.on .toggle-track { background: var(--accent-2); box-shadow: 0 0 16px var(--accent-2-glow); }
.toggle-text { font-weight: 600; color: var(--text); font-size: 0.95rem; }
.toggle-text .val { font-family: var(--mono); color: var(--accent); }

button.btn {
  font-family: var(--sans);
  font-weight: 700;
  font-size: 0.95rem;
  color: var(--bg);
  background: var(--accent);
  border: none;
  border-radius: 10px;
  padding: 10px 20px;
  cursor: pointer;
  transition: opacity 0.15s ease, transform 0.1s ease;
}
button.btn:hover { opacity: 0.88; }
button.btn:active { transform: scale(0.97); }
button.btn.secondary {
  background: transparent;
  color: var(--text);
  border: 1px solid var(--border);
}

/* ---------- Wires / bulbs / LEDs (SVG) ---------- */
.wire { stroke: var(--off); stroke-width: 4; fill: none; transition: stroke 0.2s ease, filter 0.2s ease; }
.wire.on { stroke: var(--on); filter: drop-shadow(0 0 4px var(--on-glow)); }

.pin { fill: var(--off); transition: fill 0.2s ease; }
.pin.on { fill: var(--on); filter: drop-shadow(0 0 5px var(--on-glow)); }

.gate-shape { fill: var(--bg-panel-2); stroke: var(--text-faint); stroke-width: 2.5; transition: stroke 0.2s ease; }
.gate-shape.on { stroke: var(--on); filter: drop-shadow(0 0 6px var(--on-glow)); }
.gate-label { fill: var(--text-dim); font-family: var(--sans); font-size: 13px; font-weight: 700; text-anchor: middle; }

.bulb-glass { fill: #1c2430; stroke: var(--text-faint); stroke-width: 2; transition: fill 0.25s ease, stroke 0.25s ease; }
.bulb-glass.on { fill: #fff3c4; stroke: var(--on); filter: drop-shadow(0 0 18px var(--on-glow)); }
.bulb-filament { stroke: var(--text-faint); stroke-width: 2; fill: none; transition: stroke 0.25s ease; }
.bulb-filament.on { stroke: #7a5a00; }

/* ---------- Input / output color coding (so you can see at a glance which is which) ---------- */
.wire.input-a.on { stroke: var(--accent); filter: drop-shadow(0 0 4px var(--accent-glow)); }
.pin.input-a.on { fill: var(--accent); filter: drop-shadow(0 0 5px var(--accent-glow)); }
.wire.input-b.on { stroke: var(--accent-2); filter: drop-shadow(0 0 4px var(--accent-2-glow)); }
.pin.input-b.on { fill: var(--accent-2); filter: drop-shadow(0 0 5px var(--accent-2-glow)); }
.wire.output-sum.on { stroke: var(--good); filter: drop-shadow(0 0 4px var(--good-glow)); }
.pin.output-sum.on { fill: var(--good); filter: drop-shadow(0 0 5px var(--good-glow)); }
.bulb-glass.output-sum.on { fill: #d1fae5; stroke: var(--good); filter: drop-shadow(0 0 18px var(--good-glow)); }

.legend-key {
  display: flex;
  justify-content: center;
  flex-wrap: wrap;
  gap: 18px;
  margin: 4px 0 18px;
  font-size: 0.82rem;
  color: var(--text-dim);
}
.legend-key span { display: inline-flex; align-items: center; gap: 7px; }
.legend-key i {
  display: inline-block;
  width: 10px;
  height: 10px;
  border-radius: 50%;
  flex-shrink: 0;
}

/* ---------- Truth tables ---------- */
table.truth {
  border-collapse: collapse;
  margin: 20px auto;
  font-family: var(--mono);
  font-size: 0.95rem;
}
table.truth th, table.truth td {
  border: 1px solid var(--border);
  padding: 8px 18px;
  text-align: center;
}
table.truth th { color: var(--text-faint); font-weight: 600; background: var(--bg-panel-2); }
table.truth td { color: var(--text-dim); }
table.truth tr.active-row td { background: rgba(255, 204, 77, 0.12); color: var(--text); font-weight: 700; }

/* ---------- Callouts ---------- */
.callout {
  border-left: 3px solid var(--accent);
  background: var(--bg-panel);
  padding: 16px 20px;
  border-radius: 0 10px 10px 0;
  margin: 24px 0;
}
.callout p { margin: 0; color: var(--text); font-size: 0.98rem; }
.callout.tip { border-left-color: var(--good); }

/* ---------- Prev/Next footer nav ---------- */
.pagenav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 56px;
  padding-top: 24px;
  border-top: 1px solid var(--border);
  gap: 12px;
}
.pagenav a {
  color: var(--text);
  font-weight: 600;
  padding: 10px 18px;
  border: 1px solid var(--border);
  border-radius: 10px;
}
.pagenav a:hover { border-color: var(--accent); text-decoration: none; }
.pagenav .spacer { flex: 1; }

/* ---------- Footer ---------- */
.site-footer {
  text-align: center;
  color: var(--text-faint);
  font-size: 0.85rem;
  margin-top: 56px;
  padding: 24px 0;
  border-top: 1px solid var(--border);
}

/* ---------- Misc ---------- */
.center { text-align: center; }
.row { display: flex; gap: 24px; align-items: center; justify-content: center; flex-wrap: wrap; }
.big-number {
  font-family: var(--mono);
  font-size: 3rem;
  font-weight: 700;
  color: var(--good);
  text-shadow: 0 0 24px var(--good-glow);
}
.bit-label { font-family: var(--mono); color: var(--text-faint); font-size: 0.85rem; text-align: center; margin-top: 6px; }

.two-col {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 24px;
}
@media (max-width: 640px) {
  .two-col { grid-template-columns: 1fr; }
  .steps { display: none; }
}