:root {
  --bg: #0b0f1a;
  --bg2: #121828;
  --panel: #161e31;
  --line: #26304a;
  --text: #e8ecf6;
  --muted: #8d98b5;
  --accent: #7c8cff;

  --sigmoid: #ff6b9d;
  --tanh: #ffb547;
  --relu: #4ade80;
  --leaky: #2dd4bf;
  --elu: #60a5fa;
  --swish: #c084fc;
  --softmax: #f97362;

  --c0: #60a5fa;
  --c1: #ff9f43;
  --ok: #4ade80;
  --bad: #ff6b6b;

  --head: "Space Grotesk", system-ui, sans-serif;
  --body: "IBM Plex Sans", system-ui, sans-serif;
  --mono: "JetBrains Mono", ui-monospace, monospace;
}

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

html, body {
  height: 100%;
  overflow: hidden;
  background: radial-gradient(ellipse at 20% 0%, #1a2240 0%, var(--bg) 60%) fixed, var(--bg);
  color: var(--text);
  font-family: var(--body);
}

/* ---------- Deck (fixed 16:9 stage, scaled to fit) ---------- */
.deck {
  position: absolute;
  left: 50%; top: 50%;
  width: 1280px; height: 720px;
  transform: translate(-50%, -50%) scale(var(--scale, 1));
  transform-origin: center;
}

.slide {
  position: absolute;
  inset: 0;
  padding: 48px 64px 64px;
  opacity: 0;
  transform: translateX(48px);
  transition: opacity .45s ease, transform .45s cubic-bezier(.2,.7,.2,1);
  pointer-events: none;
  font-size: 19px;
  line-height: 1.5;
}
.slide.past { transform: translateX(-48px); }
.slide.active { opacity: 1; transform: none; pointer-events: auto; }

.slide.active > * { animation: rise .55s cubic-bezier(.2,.7,.2,1) both; }
.slide.active > *:nth-child(2) { animation-delay: .05s; }
.slide.active > *:nth-child(3) { animation-delay: .12s; }
.slide.active > *:nth-child(4) { animation-delay: .18s; }
@keyframes rise { from { opacity: 0; transform: translateY(14px); } to { opacity: 1; transform: none; } }

/* ---------- Typography ---------- */
.kicker {
  font-family: var(--mono);
  font-size: 13px;
  letter-spacing: .12em;
  text-transform: uppercase;
  color: var(--accent);
  margin-bottom: 8px;
}
h1, h2, h3 { font-family: var(--head); font-weight: 700; letter-spacing: -.01em; }
h2 { font-size: 40px; margin-bottom: 26px; display: flex; align-items: center; gap: 14px; }
h2 small { font-family: var(--body); font-weight: 400; font-size: 18px; color: var(--muted); margin-top: 10px; }
h3 { font-size: 21px; margin: 4px 0 12px; color: #fff; }
b { color: #fff; font-weight: 600; }
em { color: #c9d2ff; }
.lead { font-size: 20px; margin-bottom: 14px; }
.note { color: var(--muted); font-size: 16px; margin: 10px 0; }
.note.center { text-align: center; margin-top: 22px; }
.muted { color: var(--muted); font-size: 13px; }
kbd {
  font-family: var(--mono); font-size: 12px;
  padding: 2px 7px; border: 1px solid var(--line); border-bottom-width: 2px;
  border-radius: 5px; background: var(--panel);
}

.dot {
  display: inline-block; width: 16px; height: 16px; border-radius: 50%;
  background: var(--c); box-shadow: 0 0 16px var(--c);
  flex: none;
}

/* ---------- Layout helpers ---------- */
.cols { display: grid; gap: 44px; align-items: start; }
.cols-even { grid-template-columns: 1fr 1fr; }
.fn-cols { grid-template-columns: 1fr 480px; gap: 36px; }

.formula {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 6px 18px;
  margin: 8px 0 14px;
  font-size: 19px;
  overflow: hidden;
}
.formula.left .katex-display { text-align: left; }
.formula .katex-display { margin: .6em 0; }

.callout {
  border-left: 4px solid var(--accent);
  background: color-mix(in srgb, var(--accent) 10%, transparent);
  padding: 12px 16px; border-radius: 0 10px 10px 0;
  margin: 14px 0; font-size: 17px;
}
.callout.warn { border-color: var(--bad); background: color-mix(in srgb, var(--bad) 10%, transparent); }
.callout.ok { border-color: var(--ok); background: color-mix(in srgb, var(--ok) 10%, transparent); }

.bullets { list-style: none; margin-bottom: 18px; }
.bullets li { padding-left: 22px; position: relative; margin: 7px 0; font-size: 18px; }
.bullets li::before { content: ""; position: absolute; left: 4px; top: 11px; width: 7px; height: 7px; border-radius: 2px; background: var(--accent); }

/* ---------- Beginner helpers: examples, analogies ---------- */
.example {
  background: var(--panel); border: 1px solid var(--line); border-radius: 14px;
  padding: 16px 20px; margin-bottom: 12px;
}
.ex-title { font-family: var(--head); font-weight: 700; font-size: 19px; margin-bottom: 12px; color: var(--tanh); }
.calc {
  font-family: var(--mono); font-size: 16px;
  background: var(--bg2); border-radius: 8px; padding: 7px 12px; margin: 6px 0 10px;
}
.calc b { color: var(--relu); }
.calc.result { color: var(--bad); font-weight: 600; border: 1px dashed var(--bad); }
.calc.big { font-size: 18px; text-align: center; padding: 12px; color: var(--sigmoid); }

.analogy {
  background: linear-gradient(135deg, color-mix(in srgb, var(--tanh) 12%, var(--panel)), var(--panel));
  border: 1px solid color-mix(in srgb, var(--tanh) 35%, var(--line));
  border-radius: 14px; padding: 16px 20px; margin-bottom: 14px;
}
.analogy p { font-size: 17px; margin-top: 6px; }
.an-title { font-family: var(--head); font-weight: 700; font-size: 19px; color: var(--tanh); }
.analogy.small { margin-top: 14px; padding: 12px 18px; }
.analogy.small p { font-size: 16px; }


.oneliner {
  font-size: 18px; padding: 10px 16px; border-radius: 10px; margin-bottom: 4px;
  background: color-mix(in srgb, var(--c) 12%, transparent);
  border-left: 4px solid var(--c);
}
.oneliner > b:first-child { color: var(--c); }

/* ---------- Title slide ---------- */
.title-slide { padding: 0; }
.bg-plot { position: absolute; inset: 0; opacity: .28; }
.slide.active > .bg-plot { animation: fade .8s both; }
@keyframes fade { from { opacity: 0; } to { opacity: .28; } }
.title-content { position: absolute; left: 96px; top: 150px; }
h1 { font-size: 92px; line-height: 1; margin: 14px 0 22px; }
.grad {
  background: linear-gradient(90deg, var(--sigmoid), var(--tanh), var(--relu), var(--elu), var(--swish));
  -webkit-background-clip: text; background-clip: text; color: transparent;
}
.subtitle { font-size: 24px; color: #c4cce0; max-width: 680px; }
.chips { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 40px; max-width: 760px; }
.chip {
  font-family: var(--mono); font-size: 14px;
  padding: 6px 14px; border-radius: 999px;
  border: 1px solid color-mix(in srgb, var(--c) 60%, transparent);
  color: var(--c); background: color-mix(in srgb, var(--c) 10%, var(--bg));
}
.hint { position: absolute; bottom: 70px; left: 96px; color: var(--muted); font-size: 14px; }

/* ---------- Plan ---------- */
.plan { list-style: none; display: grid; grid-template-columns: 1fr 1fr; gap: 18px 40px; margin-top: 20px; }
.plan li {
  display: flex; gap: 18px; align-items: center;
  background: var(--panel); border: 1px solid var(--line); border-radius: 14px; padding: 20px 22px;
}
.plan span { font-family: var(--mono); font-size: 28px; color: var(--accent); font-weight: 600; }
.plan b { display: block; font-size: 20px; }
.plan small { color: var(--muted); font-size: 15px; }

/* ---------- Neuron SVG ---------- */
.step { display: flex; gap: 14px; margin-bottom: 6px; }
.step .num {
  flex: none; width: 30px; height: 30px; border-radius: 50%;
  background: var(--accent); color: var(--bg); font-weight: 700;
  display: grid; place-items: center; font-size: 15px; margin-top: 2px;
}
.step > div { flex: 1; font-size: 17px; }
.nc-panel {
  background: var(--panel); border: 1px solid var(--line); border-radius: 14px;
  padding: 14px 18px 8px;
}
.nc-panel svg { width: 100%; display: block; }
.nc-panel text { fill: var(--text); text-anchor: middle; font-family: var(--body); }


.neuron .edges line { stroke: #8b98b8; stroke-width: 2; }
.neuron .in circle { fill: var(--bg2); stroke: var(--c0); stroke-width: 2; }
.neuron .in text { font-size: 20px; font-family: var(--mono); }
.neuron .in .dots { font-size: 22px; fill: var(--muted); }
.neuron .w text { fill: var(--tanh); font-size: 17px; font-family: var(--mono); }
.neuron .sum { fill: #3b4a72; stroke: #9aa8d0; stroke-width: 2; }
.neuron .act { fill: color-mix(in srgb, var(--swish) 18%, var(--bg2)); stroke: var(--swish); stroke-width: 2; }
.neuron .big { font-size: 34px; font-weight: 600; }
.neuron .f { fill: var(--swish); font-style: italic; }
.neuron .out { font-size: 28px; font-weight: 600; fill: var(--relu); }
.neuron .incap text { font-size: 13px; fill: var(--muted); font-family: var(--mono); }
.neuron .incap .fcap { fill: var(--swish); }


/* ---------- Cards ---------- */
.card-list { display: grid; gap: 12px; margin-bottom: 12px; }
.card { background: var(--panel); border: 1px solid var(--line); border-radius: 12px; padding: 12px 16px; }
.card b { display: block; font-size: 18px; color: var(--accent); }
.card span { font-size: 16px; color: #c4cce0; }
.card span b { display: inline; font-size: inherit; color: #fff; }
.card.fn > b { color: var(--c); }
.card.good b { color: var(--ok); }
.card.bad > b { color: var(--bad); }

/* ---------- XOR ---------- */
.truth { border-collapse: collapse; margin: 8px 0 16px; font-family: var(--mono); font-size: 17px; }
.truth th, .truth td { padding: 7px 22px; text-align: center; border-bottom: 1px solid var(--line); }
.truth th { color: var(--muted); font-weight: 400; font-family: var(--body); }
.truth .c0 { color: var(--c0); font-weight: 600; }
.truth .c1 { color: var(--c1); font-weight: 600; }
.xor-pair { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; align-items: start; }
.xor-box { display: flex; flex-direction: column; align-items: center; gap: 12px; }
.xor-box svg { width: 100%; background: var(--panel); border: 1px solid var(--line); border-radius: 14px; }
.xor-score { font-size: 17px; }
.xor-score b { font-family: var(--mono); font-size: 22px; }

.btn {
  font: 600 16px var(--body); color: var(--bg); background: var(--accent);
  border: 0; border-radius: 10px; padding: 11px 20px; cursor: pointer;
  transition: transform .15s, filter .15s;
}
.btn:hover { filter: brightness(1.1); transform: translateY(-1px); }

/* ---------- Plots ---------- */
canvas.plot { display: block; border-radius: 14px; }
.cols canvas.plot { background: var(--panel); border: 1px solid var(--line); }

.controls { display: flex; flex-direction: column; gap: 10px; }
.toggle {
  font: 600 16px var(--body); text-align: left;
  padding: 10px 14px; border-radius: 10px; cursor: pointer;
  background: transparent; color: var(--muted);
  border: 1px solid var(--line); display: flex; align-items: center; gap: 10px;
  transition: all .2s;
}
.toggle::before { content: ""; width: 12px; height: 12px; border-radius: 50%; border: 2px solid var(--c); transition: all .2s; }
.toggle.on { color: #fff; border-color: color-mix(in srgb, var(--c) 60%, transparent); background: color-mix(in srgb, var(--c) 12%, transparent); }
.toggle.on::before { background: var(--c); box-shadow: 0 0 10px var(--c); }

.switch { display: flex; align-items: center; gap: 10px; font-size: 16px; cursor: pointer; margin-top: 6px; }
.switch input { display: none; }
.switch span { width: 40px; height: 22px; border-radius: 999px; background: var(--line); position: relative; transition: background .2s; }
.switch span::after { content: ""; position: absolute; left: 3px; top: 3px; width: 16px; height: 16px; border-radius: 50%; background: #fff; transition: transform .2s; }
.switch input:checked + span { background: var(--accent); }
.switch input:checked + span::after { transform: translateX(18px); }

/* ---------- Function slides ---------- */
.fn-slide h2 { color: var(--c); }
.fn-slide .formula { border-color: color-mix(in srgb, var(--c) 40%, var(--line)); font-size: 19px; margin: 10px 0; }
.pc { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; }
.pc h4 { font-family: var(--mono); font-size: 13px; letter-spacing: .1em; text-transform: uppercase; margin-bottom: 6px; }
.pros h4 { color: var(--ok); }
.cons h4 { color: var(--bad); }
.pc ul { list-style: none; }
.pc li { font-size: 15.5px; line-height: 1.4; padding-left: 22px; position: relative; margin-bottom: 7px; color: #d3d9e8; }
.pros li::before { content: "✓"; position: absolute; left: 0; color: var(--ok); font-weight: 700; }
.cons li::before { content: "✗"; position: absolute; left: 0; color: var(--bad); font-weight: 700; }
.usage {
  margin-top: 8px; font-size: 15.5px; padding: 9px 14px; border-radius: 10px;
  background: color-mix(in srgb, var(--c) 9%, transparent);
  border: 1px solid color-mix(in srgb, var(--c) 30%, transparent);
}

/* ---------- Comparison table ---------- */

/* ---------- Vanishing gradient ---------- */
.vg { display: flex; flex-direction: column; gap: 12px; }
.vg-controls { display: flex; gap: 24px; align-items: center; justify-content: space-between; }
.seg { display: inline-flex; background: var(--panel); border: 1px solid var(--line); border-radius: 10px; padding: 3px; }
.seg button {
  font: 600 15px var(--body); color: var(--muted); background: none; border: 0;
  padding: 7px 14px; border-radius: 8px; cursor: pointer; transition: all .2s;
}
.seg button.on { color: var(--bg); background: var(--c); }
.range { display: flex; align-items: center; gap: 10px; font-size: 15px; color: var(--muted); }
.range b { color: #fff; font-family: var(--mono); }
input[type=range] { width: 200px; accent-color: var(--accent); }
#vgCanvas { background: var(--panel); border: 1px solid var(--line); border-radius: 14px; }
.vg-readout { font-size: 18px; }
.vg-readout b { font-family: var(--mono); font-size: 22px; }

/* ---------- Solutions ---------- */

/* ---------- Softmax ---------- */
.sm { background: var(--panel); border: 1px solid var(--line); border-radius: 14px; padding: 18px 22px; }
.sm-row { display: grid; grid-template-columns: 118px 150px 1fr; gap: 14px; align-items: center; margin: 12px 0; }
.sm-row .lbl { font-weight: 600; white-space: nowrap; }
.sm-row .z { display: flex; flex-direction: column; font-family: var(--mono); font-size: 13px; color: var(--muted); }
.sm-row .z input { width: 150px; }
.sm-bar { height: 38px; background: var(--bg2); border-radius: 8px; position: relative; overflow: hidden; }
.sm-bar div {
  height: 100%; width: 0; border-radius: 8px;
  background: linear-gradient(90deg, color-mix(in srgb, var(--softmax) 70%, #000), var(--softmax));
  transition: width .25s ease;
}
.sm-bar.top div { background: linear-gradient(90deg, #d9534f, #ffb547); }
.sm-bar span { position: absolute; right: 10px; top: 50%; transform: translateY(-50%); font-family: var(--mono); font-size: 15px; font-weight: 600; }
.sm-sum { margin-top: 14px; font-size: 16px; color: var(--muted); }
.sm-sum b { font-family: var(--mono); }


/* ---------- Choose ---------- */
.choose { display: grid; grid-template-columns: 1fr 1fr; gap: 40px; }
.ch {
  display: flex; justify-content: space-between; align-items: center; gap: 16px;
  padding: 14px 18px; margin-bottom: 12px; border-radius: 12px;
  background: var(--panel); border: 1px solid var(--line); border-left: 4px solid var(--c);
}
.ch span { color: #c4cce0; font-size: 17px; }
.ch b { color: var(--c); font-family: var(--head); font-size: 19px; text-align: right; }

/* ---------- Glossary ---------- */

/* ---------- Conclusion ---------- */
.takeaways { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; }
.takeaways > div { display: flex; gap: 16px; background: var(--panel); border: 1px solid var(--line); border-radius: 14px; padding: 18px 20px; }
.takeaways span { font-family: var(--head); font-size: 34px; font-weight: 700; color: var(--accent); line-height: 1; }
.takeaways p { font-size: 17.5px; }
.thanks { margin-top: 44px; text-align: center; font-family: var(--head); font-size: 46px; font-weight: 700; }
.thanks span { color: var(--muted); font-size: 26px; font-weight: 500; margin-left: 10px; }

/* ---------- HUD ---------- */
.hud {
  position: fixed; right: 20px; bottom: 16px;
  display: flex; align-items: center; gap: 10px;
  font-family: var(--mono); font-size: 13px; color: var(--muted);
  z-index: 10;
}
.progress { position: fixed; left: 0; right: 0; bottom: 0; height: 3px; background: transparent; }
#progressBar { height: 100%; width: 0; background: linear-gradient(90deg, var(--sigmoid), var(--tanh), var(--relu), var(--elu), var(--swish)); transition: width .4s ease; }
.nav {
  width: 32px; height: 32px; border-radius: 8px; border: 1px solid var(--line);
  background: var(--panel); color: var(--text); font-size: 20px; line-height: 1; cursor: pointer;
}
.nav:hover { border-color: var(--accent); }