:root {
  --paper: #f2ebda;
  --paper-deep: #e4d9bd;
  --ink: #172126;
  --muted: #5f6968;
  --cyan: #047f87;
  --cyan-light: #b8e2df;
  --rust: #a4472d;
  --line: rgba(23, 33, 38, 0.18);
  --shadow: 0 18px 50px rgba(29, 37, 38, 0.14);
  --radius: 3px;
  --body: "Iowan Old Style", "Palatino Linotype", Palatino, serif;
  --display: "Avenir Next Condensed", "DIN Condensed", "Franklin Gothic Condensed", sans-serif;
  --mono: "IBM Plex Mono", "SFMono-Regular", Consolas, monospace;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  color: var(--ink);
  background:
    radial-gradient(circle at 82% 7%, rgba(4, 127, 135, 0.13), transparent 26rem),
    repeating-linear-gradient(0deg, transparent 0 31px, rgba(23, 33, 38, 0.045) 31px 32px),
    var(--paper);
  font-family: var(--body);
  font-size: 18px;
  line-height: 1.62;
}

a { color: var(--cyan); text-underline-offset: 0.18em; }
a:hover { color: var(--rust); }

.page {
  width: min(1080px, calc(100% - 32px));
  margin: 0 auto;
  padding: 36px 0 90px;
}

.course-nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 18px;
  margin-bottom: 48px;
  font: 700 0.76rem/1 var(--mono);
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.course-nav a { text-decoration: none; }
.course-mark { display: flex; align-items: center; gap: 10px; }
.course-mark::before {
  content: "";
  width: 12px;
  height: 12px;
  border: 2px solid var(--cyan);
  border-radius: 50%;
  box-shadow: 7px 0 0 -4px var(--paper), 7px 0 0 -2px var(--rust);
}

.hero {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(220px, 0.38fr);
  gap: clamp(32px, 6vw, 88px);
  align-items: end;
  padding: 22px 0 54px;
  border-bottom: 1px solid var(--line);
}

.eyebrow {
  margin: 0 0 12px;
  color: var(--rust);
  font: 700 0.75rem/1.2 var(--mono);
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

h1, h2, h3 {
  font-family: var(--display);
  font-weight: 800;
  letter-spacing: -0.025em;
  line-height: 0.98;
}

h1 { margin: 0; max-width: 760px; font-size: clamp(3.3rem, 9vw, 7.6rem); }
h2 { margin: 0 0 22px; font-size: clamp(2rem, 5vw, 3.5rem); }
h3 { margin: 0 0 12px; font-size: 1.35rem; line-height: 1.15; }

.lede { max-width: 700px; margin: 24px 0 0; font-size: clamp(1.1rem, 2.3vw, 1.42rem); line-height: 1.45; }

.lesson-meta {
  border-left: 3px solid var(--cyan);
  padding: 4px 0 4px 18px;
  color: var(--muted);
  font: 0.78rem/1.6 var(--mono);
}

.lesson-meta strong { color: var(--ink); }

.section {
  display: grid;
  grid-template-columns: minmax(140px, 0.28fr) minmax(0, 0.72fr);
  gap: clamp(28px, 6vw, 80px);
  padding: 66px 0;
  border-bottom: 1px solid var(--line);
}

.section-index {
  color: var(--cyan);
  font: 700 0.72rem/1.2 var(--mono);
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.section-index span { display: block; margin-top: 12px; color: var(--muted); letter-spacing: 0; text-transform: none; }
.prose { max-width: 720px; }
.prose > :first-child { margin-top: 0; }
.prose p { margin: 0 0 1.15em; }

.big-idea {
  margin: 30px 0;
  padding: 24px 28px;
  border: 1px solid var(--ink);
  background: rgba(255,255,255,0.24);
  box-shadow: 7px 7px 0 var(--cyan-light);
  font-size: 1.18rem;
}

.equation {
  overflow-x: auto;
  margin: 28px 0;
  padding: 24px;
  color: #eaf8f7;
  background: var(--ink);
  font: 700 clamp(1.1rem, 3vw, 1.55rem)/1.4 var(--mono);
  text-align: center;
  white-space: nowrap;
}

.equation small { display: block; margin-top: 8px; color: #a9bfbd; font: 400 0.72rem/1.4 var(--mono); white-space: normal; }

.experiment {
  position: relative;
  margin: 30px 0;
  padding: clamp(22px, 5vw, 38px);
  border: 1px solid var(--line);
  background: rgba(250, 247, 238, 0.72);
  box-shadow: var(--shadow);
}

.experiment::before {
  content: "TRY IT";
  position: absolute;
  top: -11px;
  left: 18px;
  padding: 3px 9px;
  color: var(--paper);
  background: var(--rust);
  font: 700 0.68rem/1.4 var(--mono);
  letter-spacing: 0.12em;
}

.controls { display: grid; grid-template-columns: repeat(3, 1fr); gap: 14px; margin: 22px 0; }
label { display: grid; gap: 6px; color: var(--muted); font: 700 0.75rem/1.2 var(--mono); }

input, select, button {
  width: 100%;
  min-height: 44px;
  border: 1px solid var(--ink);
  border-radius: var(--radius);
  color: var(--ink);
  background: #faf7ee;
  font: 700 1rem/1 var(--mono);
}

input, select { padding: 10px 12px; }
button { cursor: pointer; padding: 10px 14px; transition: transform 120ms ease, background 120ms ease, color 120ms ease; }
button:hover { transform: translateY(-2px); }
button:focus-visible, input:focus-visible, select:focus-visible, a:focus-visible { outline: 3px solid var(--cyan-light); outline-offset: 3px; }

.result {
  min-height: 64px;
  display: grid;
  place-items: center;
  padding: 14px;
  color: #effafa;
  background: var(--cyan);
  font: 800 clamp(1.2rem, 4vw, 2rem)/1.2 var(--mono);
  text-align: center;
}

.clock {
  position: relative;
  width: min(100%, 380px);
  aspect-ratio: 1;
  margin: 32px auto;
  border: 2px solid var(--ink);
  border-radius: 50%;
  background: radial-gradient(circle, var(--paper) 0 7%, transparent 7.5%), rgba(184, 226, 223, 0.22);
}

.clock-node {
  position: absolute;
  left: 50%;
  top: 50%;
  display: grid;
  width: 42px;
  height: 42px;
  place-items: center;
  margin: -21px;
  border: 1px solid var(--ink);
  border-radius: 50%;
  background: var(--paper);
  font: 700 0.88rem/1 var(--mono);
  transform: rotate(var(--angle)) translateY(-150px) rotate(calc(-1 * var(--angle)));
  transition: background 180ms ease, color 180ms ease, transform 180ms ease;
}

.clock-node.active { color: white; background: var(--rust); transform: rotate(var(--angle)) translateY(-150px) rotate(calc(-1 * var(--angle))) scale(1.18); }

.clock.dense .clock-node {
  width: 34px;
  height: 34px;
  margin: -17px;
  font-size: 0.76rem;
}

.clock.dense .clock-node.active {
  transform: rotate(var(--angle)) translateY(-150px) rotate(calc(-1 * var(--angle))) scale(1.1);
}

.quiz { margin-top: 30px; }
.quiz-options { display: grid; grid-template-columns: repeat(4, 1fr); gap: 10px; margin: 16px 0; }
.quiz-options button[aria-pressed="true"] { color: white; background: var(--cyan); }
.feedback { min-height: 32px; color: var(--rust); font: 700 0.86rem/1.5 var(--mono); }
.feedback.correct { color: var(--cyan); }

.answer-key {
  margin: 26px 0 30px;
  border: 1px solid var(--ink);
  background: rgba(250, 247, 238, 0.72);
  box-shadow: 6px 6px 0 var(--cyan-light);
}

.answer-key summary {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr);
  gap: 14px;
  align-items: center;
  padding: 18px 20px;
  cursor: pointer;
  list-style: none;
  font: 800 0.84rem/1.45 var(--mono);
}

.answer-key summary::-webkit-details-marker { display: none; }

.answer-key summary::before {
  content: "+";
  display: grid;
  width: 28px;
  height: 28px;
  place-items: center;
  border-radius: 50%;
  color: var(--paper);
  background: var(--cyan);
  font-size: 1.15rem;
  transition: transform 160ms ease, background 160ms ease;
}

.answer-key[open] summary::before {
  content: "−";
  background: var(--rust);
  transform: rotate(180deg);
}

.answer-key summary:hover::before { transform: scale(1.08); }
.answer-key[open] summary:hover::before { transform: rotate(180deg) scale(1.08); }
.answer-key summary:focus-visible { outline: 3px solid var(--cyan-light); outline-offset: 3px; }

.answer-key-body {
  padding: 4px 24px 24px 58px;
  border-top: 1px solid var(--line);
}

.answer-key-body > p:first-child {
  margin-top: 20px;
  color: var(--muted);
  font: 0.78rem/1.55 var(--mono);
}

.answer-key-body ol { padding-left: 1.35em; }
.answer-key-body li { margin: 0 0 22px; padding-left: 7px; }
.answer-key-body li:last-child { margin-bottom: 0; }
.answer-key-body li::marker { color: var(--rust); font: 800 0.85rem var(--mono); }
.answer-key-body li p { margin: 0 0 8px; }

.answer-note {
  padding: 10px 13px;
  border-left: 3px solid var(--rust);
  color: var(--muted);
  background: rgba(164, 71, 45, 0.06);
  font-size: 0.92rem;
}

.field-note {
  margin: 28px 0;
  padding: 18px 22px;
  border-left: 4px solid var(--rust);
  background: rgba(164, 71, 45, 0.07);
}

.source-list { padding-left: 1.2em; }
.source-list li { margin: 0 0 12px; }
.tiny { color: var(--muted); font: 0.78rem/1.55 var(--mono); }

.rule-list {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 1px;
  margin: 28px 0;
  padding: 1px;
  background: var(--line);
}

.rule-list > div {
  padding: 20px;
  background: rgba(250, 247, 238, 0.92);
}

.rule-list strong {
  display: block;
  margin-bottom: 6px;
  color: var(--cyan);
  font: 800 0.8rem/1.2 var(--mono);
  text-transform: uppercase;
  letter-spacing: 0.08em;
}

.curve-stage {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(190px, 0.42fr);
  gap: 26px;
  align-items: center;
  margin: 24px 0;
}

.curve-plot {
  width: 100%;
  height: auto;
  aspect-ratio: 1;
  overflow: visible;
  border: 1px solid var(--line);
  background:
    linear-gradient(rgba(23, 33, 38, 0.05) 1px, transparent 1px),
    linear-gradient(90deg, rgba(23, 33, 38, 0.05) 1px, transparent 1px),
    rgba(242, 235, 218, 0.68);
  background-size: calc(100% / 17) calc(100% / 17);
}

.curve-point {
  fill: var(--cyan);
  opacity: 0.52;
  transition: r 160ms ease, fill 160ms ease, opacity 160ms ease;
}

.curve-point.trail { fill: var(--ink); opacity: 0.9; }
.curve-point.active { fill: var(--rust); opacity: 1; }

.curve-readout {
  display: grid;
  gap: 14px;
  font: 0.78rem/1.5 var(--mono);
}

.curve-readout output {
  display: block;
  color: var(--paper);
  background: var(--ink);
  padding: 18px;
  font: 800 1.35rem/1.2 var(--mono);
  text-align: center;
}

.curve-readout ol {
  max-height: 250px;
  overflow: auto;
  margin: 0;
  padding: 12px 12px 12px 40px;
  border: 1px solid var(--line);
  background: rgba(250, 247, 238, 0.72);
}

.curve-readout li.active { color: var(--rust); font-weight: 800; }

.worked-steps {
  display: grid;
  gap: 8px;
  margin: 28px 0;
  counter-reset: work;
}

.worked-steps p {
  position: relative;
  margin: 0;
  padding: 15px 18px 15px 58px;
  border-left: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.2);
  font-family: var(--mono);
  font-size: 0.88rem;
}

.worked-steps p::before {
  counter-increment: work;
  content: counter(work, decimal-leading-zero);
  position: absolute;
  left: 16px;
  color: var(--cyan);
  font-weight: 800;
}

.key-flow {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  gap: 16px;
  align-items: stretch;
  margin: 26px 0;
}

.key-box {
  display: grid;
  align-content: center;
  min-height: 128px;
  padding: 20px;
  border: 1px solid var(--ink);
  background: rgba(250, 247, 238, 0.86);
  text-align: center;
}

.key-box span {
  color: var(--muted);
  font: 700 0.7rem/1.2 var(--mono);
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.key-box output {
  margin-top: 10px;
  color: var(--ink);
  font: 800 clamp(1.1rem, 3vw, 1.65rem)/1.2 var(--mono);
}

.key-box.public { color: var(--paper); background: var(--ink); }
.key-box.public span { color: #a9bfbd; }
.key-box.public output { color: #eaf8f7; }

.flow-arrow {
  display: grid;
  place-items: center;
  min-width: 80px;
  color: var(--rust);
  font: 800 0.75rem/1.3 var(--mono);
  text-align: center;
}

.flow-arrow::after { content: "→"; display: block; font-size: 2rem; line-height: 1; }

.binary-strip {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin: 18px 0;
}

.binary-bit {
  min-width: 80px;
  padding: 10px 12px;
  border: 1px solid var(--line);
  color: var(--muted);
  background: rgba(250, 247, 238, 0.72);
  font: 700 0.76rem/1.3 var(--mono);
  text-align: center;
}

.binary-bit.active {
  border-color: var(--cyan);
  color: var(--ink);
  background: var(--cyan-light);
}

.attack-panel {
  display: grid;
  grid-template-columns: minmax(0, 0.56fr) minmax(220px, 0.44fr);
  gap: 20px;
  align-items: start;
  margin-top: 24px;
}

.attack-log {
  min-height: 230px;
  max-height: 330px;
  overflow: auto;
  margin: 0;
  padding: 12px;
  border: 1px solid var(--line);
  background: rgba(250, 247, 238, 0.72);
  font: 0.78rem/1.5 var(--mono);
  list-style: none;
}

.attack-log li {
  display: grid;
  grid-template-columns: 72px 1fr;
  gap: 10px;
  padding: 7px 8px;
  border-bottom: 1px solid var(--line);
}

.attack-log li.found { color: white; background: var(--rust); }
.attack-status { min-height: 52px; margin-top: 14px; color: var(--cyan); font: 800 0.86rem/1.45 var(--mono); }

.tangent-stage {
  margin: 24px 0;
  border: 1px solid var(--line);
  background: rgba(242, 235, 218, 0.72);
}

.tangent-plot {
  display: block;
  width: 100%;
  height: auto;
  aspect-ratio: 7 / 4.6;
}

.plot-axis { stroke: rgba(23, 33, 38, 0.34); stroke-width: 1; }
.plot-grid { stroke: rgba(23, 33, 38, 0.08); stroke-width: 1; }
.plot-curve { fill: none; stroke: var(--cyan); stroke-width: 3; }
.plot-tangent { stroke: var(--rust); stroke-width: 2.5; }
.plot-reflection { stroke: var(--muted); stroke-width: 1.5; stroke-dasharray: 6 6; }
.plot-point { stroke: var(--paper); stroke-width: 2; }
.plot-point.p { fill: var(--ink); }
.plot-point.r { fill: var(--rust); }
.plot-point.sum { fill: var(--cyan); }
.plot-label { fill: var(--ink); font: 700 16px var(--mono); paint-order: stroke; stroke: var(--paper); stroke-width: 4px; }

.formula-readout {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 1px;
  margin: 0;
  background: var(--line);
}

.formula-readout > div {
  min-width: 0;
  padding: 14px;
  background: rgba(250, 247, 238, 0.92);
}

.formula-readout span {
  display: block;
  margin-bottom: 6px;
  color: var(--muted);
  font: 700 0.66rem/1.2 var(--mono);
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.formula-readout output {
  color: var(--ink);
  font: 800 0.82rem/1.35 var(--mono);
}

.coefficient-table {
  width: 100%;
  margin: 24px 0;
  border-collapse: collapse;
  font-family: var(--mono);
  font-size: 0.82rem;
}

.coefficient-table th,
.coefficient-table td {
  padding: 13px 15px;
  border: 1px solid var(--line);
  text-align: left;
}

.coefficient-table th { color: var(--paper); background: var(--ink); }
.coefficient-table td { background: rgba(250, 247, 238, 0.72); }

.signature-lab {
  display: grid;
  gap: 22px;
}

.signature-stage {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 1px;
  background: var(--line);
  border: 1px solid var(--line);
}

.signature-card {
  min-width: 0;
  padding: 20px;
  background: rgba(250, 247, 238, 0.94);
}

.signature-card.public { color: var(--paper); background: var(--ink); }
.signature-card h3 { font-size: 1.1rem; }
.signature-card p { margin: 8px 0 0; }
.signature-card output { display: block; margin-top: 10px; font: 800 0.9rem/1.45 var(--mono); overflow-wrap: anywhere; }
.signature-card.public output { color: #eaf8f7; }

.verify-status {
  min-height: 74px;
  display: grid;
  place-items: center;
  margin: 0;
  padding: 16px;
  border: 1px solid var(--ink);
  font: 800 0.9rem/1.45 var(--mono);
  text-align: center;
}

.verify-status.valid { color: white; background: var(--cyan); }
.verify-status.invalid { color: white; background: var(--rust); }

.equation-check {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  gap: 12px;
  align-items: center;
  margin: 18px 0;
  font: 800 0.82rem/1.4 var(--mono);
  text-align: center;
}

.equation-check span {
  min-width: 0;
  padding: 14px;
  background: rgba(184, 226, 223, 0.35);
  overflow-wrap: anywhere;
}

.equation-check b { color: var(--rust); }

.optional-detail {
  margin-top: 6px;
  padding: 14px 18px;
  border: 1px dashed var(--line);
  background: rgba(255,255,255,0.18);
}

.optional-detail summary { cursor: pointer; color: var(--cyan); font: 800 0.8rem/1.4 var(--mono); }

.lesson-footer { padding: 54px 0 0; }
.lesson-footer p { max-width: 700px; }

.term-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 1px; margin: 28px 0; background: var(--line); border: 1px solid var(--line); }
.term { padding: 22px; background: rgba(250, 247, 238, 0.9); }
.term dt { color: var(--cyan); font: 800 0.84rem/1.2 var(--mono); }
.term dd { margin: 8px 0 0; }

@media (max-width: 740px) {
  body { font-size: 17px; }
  .hero, .section { grid-template-columns: 1fr; }
  .hero { align-items: start; }
  .section-index span { display: inline; margin-left: 8px; }
  .controls { grid-template-columns: 1fr; }
  .curve-stage, .rule-list, .attack-panel { grid-template-columns: 1fr; }
  .key-flow { grid-template-columns: 1fr; }
  .flow-arrow::after { content: "↓"; }
  .formula-readout { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .signature-stage, .equation-check { grid-template-columns: 1fr; }
  .clock-node { transform: rotate(var(--angle)) translateY(-112px) rotate(calc(-1 * var(--angle))); }
  .clock-node.active { transform: rotate(var(--angle)) translateY(-112px) rotate(calc(-1 * var(--angle))) scale(1.15); }
  .clock.dense .clock-node.active { transform: rotate(var(--angle)) translateY(-112px) rotate(calc(-1 * var(--angle))) scale(1.08); }
  .term-grid { grid-template-columns: 1fr; }
  .answer-key-body { padding: 4px 18px 20px 28px; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { scroll-behavior: auto !important; transition: none !important; }
}

@media print {
  body { background: white; color: black; font-size: 11pt; }
  .page { width: 100%; padding: 0; }
  .experiment, .quiz { break-inside: avoid; box-shadow: none; }
  .course-nav { display: none; }
  a { color: black; }
}