:root {
  --paper: #eef1f6;
  --paper-line: #c7d1de;
  --ink: #1c2430;
  --ink-soft: #5c6b7a;
  --ink-faint: #93a2b2;
  --pen-red: #c1432e;
  --pen-red-dim: rgba(193, 66, 46, 0.16);
  --highlighter: #f4d35e;
  --marker-teal: #1f7a6c;
  --card-bg: #f8f9fb;
  --card-shadow: 0 1px 0 rgba(28, 36, 48, 0.06), 0 8px 24px -12px rgba(28, 36, 48, 0.18);
  --radius: 3px;
  --mono: 'IBM Plex Mono', ui-monospace, monospace;
  --sans: 'IBM Plex Sans', system-ui, sans-serif;
  --hand: 'Caveat', cursive;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  min-height: 100%;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--sans);
}

body {
  background-image:
    linear-gradient(var(--paper-line) 1px, transparent 1px),
    linear-gradient(90deg, var(--paper-line) 1px, transparent 1px);
  background-size: 28px 28px;
  background-position: -1px -1px;
  position: relative;
}

.grain {
  position: fixed;
  inset: 0;
  pointer-events: none;
  z-index: 999;
  opacity: 0.035;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='120' height='120'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='2' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)'/%3E%3C/svg%3E");
}

@media (prefers-reduced-motion: reduce) {
  * { animation-duration: 0.001ms !important; transition-duration: 0.001ms !important; }
}

/* ---------- Masthead ---------- */

.masthead {
  border-bottom: 2px solid var(--ink);
  background: rgba(238, 241, 246, 0.9);
  backdrop-filter: blur(4px);
  position: sticky;
  top: 0;
  z-index: 10;
}

.masthead-inner {
  max-width: 1180px;
  margin: 0 auto;
  padding: 18px 28px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  flex-wrap: wrap;
}

.brand { display: flex; align-items: baseline; gap: 12px; }

.brand-mark {
  font-family: var(--mono);
  font-size: 28px;
  font-weight: 700;
  color: var(--pen-red);
  transform: translateY(2px);
}

.brand h1 {
  font-family: var(--mono);
  font-size: 22px;
  font-weight: 600;
  letter-spacing: -0.02em;
  margin: 0;
}

.tagline {
  font-family: var(--hand);
  font-size: 19px;
  color: var(--ink-soft);
  margin: -2px 0 0;
}

.key-slot {
  display: flex;
  align-items: center;
  gap: 8px;
  font-family: var(--mono);
  font-size: 11px;
  color: var(--ink-soft);
}

.key-slot label { white-space: nowrap; }

#apiKey {
  font-family: var(--mono);
  font-size: 12px;
  padding: 7px 10px;
  border: 1.5px solid var(--ink);
  border-radius: var(--radius);
  background: #fff;
  width: 170px;
  color: var(--ink);
}

#apiKey:focus-visible { outline: 2px solid var(--marker-teal); outline-offset: 1px; }

.key-hint { font-family: var(--hand); font-size: 15px; color: var(--ink-faint); }

/* ---------- Layout ---------- */

.sheet {
  max-width: 1180px;
  margin: 0 auto;
  padding: 36px 28px 60px;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 28px;
  align-items: start;
}

@media (max-width: 900px) {
  .sheet { grid-template-columns: 1fr; }
}

.page-left, .page-right {
  display: flex;
  flex-direction: column;
  gap: 22px;
}

/* ---------- Notebook card ---------- */

.notebook {
  background: var(--card-bg);
  border: 1.5px solid var(--ink);
  border-radius: var(--radius);
  box-shadow: var(--card-shadow);
  padding: 22px 22px 20px;
  position: relative;
}

.notebook-tab {
  position: absolute;
  top: -13px;
  left: 18px;
  background: var(--highlighter);
  color: var(--ink);
  font-family: var(--mono);
  font-size: 11px;
  font-weight: 600;
  letter-spacing: 0.02em;
  padding: 3px 10px;
  border: 1.5px solid var(--ink);
  border-radius: var(--radius);
  transform: rotate(-1.2deg);
}

#problemInput {
  width: 100%;
  min-height: 190px;
  border: none;
  background: transparent;
  resize: vertical;
  font-family: var(--sans);
  font-size: 15px;
  line-height: 1.9;
  color: var(--ink);
  padding-top: 10px;
}

#problemInput:focus-visible { outline: none; }
#problemInput::placeholder { color: var(--ink-faint); }

.rule-line {
  height: 2px;
  background: repeating-linear-gradient(90deg, var(--paper-line) 0 6px, transparent 6px 12px);
  margin: 4px 0 16px;
}

.controls {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  flex-wrap: wrap;
}
.sample-picker { font-family: var(--mono); font-size: 10px; color: var(--ink-soft); display: inline-flex; align-items: center; gap: 5px; }
.sample-picker select { max-width: 118px; padding: 7px 4px; font: inherit; color: var(--ink); background: #fff; border: 1.5px solid var(--ink); border-radius: var(--radius); }
.sample-picker select:focus-visible { outline: 2px solid var(--marker-teal); outline-offset: 2px; }

.lang-toggle {
  display: inline-flex;
  border: 1.5px solid var(--ink);
  border-radius: var(--radius);
  overflow: hidden;
}

.lang-btn {
  font-family: var(--mono);
  font-size: 12px;
  font-weight: 600;
  padding: 8px 14px;
  background: #fff;
  border: none;
  color: var(--ink-soft);
  cursor: pointer;
}

.lang-btn + .lang-btn { border-left: 1.5px solid var(--ink); }
.lang-btn.active { background: var(--ink); color: var(--paper); }

.pen-btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  font-family: var(--mono);
  font-size: 13px;
  font-weight: 600;
  color: #fff;
  background: var(--pen-red);
  border: 1.5px solid var(--ink);
  border-radius: var(--radius);
  padding: 10px 18px;
  cursor: pointer;
  transition: transform 0.12s ease, box-shadow 0.12s ease;
  box-shadow: 3px 3px 0 var(--ink);
}

.pen-btn:hover { transform: translate(-1px, -1px); box-shadow: 4px 4px 0 var(--ink); }
.pen-btn:active { transform: translate(1px, 1px); box-shadow: 1px 1px 0 var(--ink); }
.pen-btn:disabled { opacity: 0.55; cursor: progress; }
.pen-btn:focus-visible { outline: 2px solid var(--marker-teal); outline-offset: 2px; }

.status-line {
  font-family: var(--hand);
  font-size: 17px;
  color: var(--marker-teal);
  min-height: 22px;
  margin: 10px 2px 0;
}
.status-line.err { color: var(--pen-red); }

/* ---------- Margin notes ---------- */

.margin-notes-card { animation: settle 0.35s ease both; }

.margin-notes-list {
  list-style: none;
  margin: 10px 0 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.margin-notes-list li {
  display: flex;
  gap: 10px;
  align-items: flex-start;
  font-size: 14px;
  line-height: 1.6;
}

.margin-notes-list .note-arrow {
  font-family: var(--hand);
  font-size: 22px;
  color: var(--pen-red);
  line-height: 1;
  transform: translateY(-2px);
}

.margin-notes-list mark {
  background: var(--highlighter);
  padding: 0 3px;
  border-radius: 2px;
}

/* ---------- Radar ---------- */

.radar-card {
  background: var(--card-bg);
  border: 1.5px solid var(--ink);
  border-radius: var(--radius);
  box-shadow: var(--card-shadow);
  padding: 22px;
  position: relative;
}

.radar-svg { width: 100%; height: auto; display: block; }

.radar-hint {
  font-family: var(--hand);
  font-size: 16px;
  color: var(--ink-faint);
  text-align: center;
  margin: 6px 0 0;
}

.node-label {
  font-family: var(--mono);
  font-size: 10.5px;
  fill: var(--ink-soft);
  text-anchor: middle;
}

.node-label.winner { fill: var(--ink); font-weight: 700; }

.node-circle { transition: r 0.5s cubic-bezier(.2,.8,.2,1), fill-opacity 0.5s ease; }

.pen-circle {
  fill: none;
  stroke: var(--pen-red);
  stroke-width: 2.5;
  stroke-linecap: round;
  filter: url(#roughen);
}

/* ---------- Template card ---------- */

.template-card { animation: settle 0.35s ease both; }

.template-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-top: 8px;
}

.pattern-pill {
  font-family: var(--mono);
  font-size: 12px;
  font-weight: 700;
  background: var(--pen-red-dim);
  color: var(--pen-red);
  border: 1px solid var(--pen-red);
  border-radius: 20px;
  padding: 4px 12px;
}

.copy-btn {
  font-family: var(--mono);
  font-size: 11px;
  border: 1.5px solid var(--ink);
  background: #fff;
  border-radius: var(--radius);
  padding: 6px 12px;
  cursor: pointer;
  color: var(--ink);
}
.copy-btn:hover { background: var(--ink); color: var(--paper); }

.template-code {
  margin-top: 12px;
  background: #14181f;
  color: #dbe3ec;
  font-family: var(--mono);
  font-size: 12.5px;
  line-height: 1.7;
  padding: 16px 18px;
  border-radius: var(--radius);
  overflow-x: auto;
  white-space: pre;
}

/* ---------- Footer ---------- */

.colophon {
  text-align: center;
  font-family: var(--mono);
  font-size: 11px;
  color: var(--ink-faint);
  padding: 20px 0 40px;
  letter-spacing: 0.03em;
}

@keyframes settle {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: translateY(0); }
}

/* ---------- Accessible interactive additions ---------- */
.sr-only { position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px; overflow: hidden; clip: rect(0, 0, 0, 0); white-space: nowrap; border: 0; }
.radar-empty { min-height: 180px; display: grid; place-content: center; text-align: center; color: var(--ink-soft); font-family: var(--hand); font-size: 20px; animation: settle .35s ease both; }
.radar-empty span { color: var(--pen-red); font-size: 30px; animation: twinkle 2s ease-in-out infinite; }
.radar-empty p { margin: 4px 0; }
.radar-svg.is-empty { display: none; }
.radar-link { stroke: #9ba8b7; stroke-width: 1.2; }
.radar-center { fill: var(--ink); }
.radar-node { cursor: pointer; outline: none; }
.radar-node .node-circle { fill: #64748b; stroke: var(--ink); stroke-width: 1.5; transition: r .65s cubic-bezier(.2,.8,.2,1), fill-opacity .5s ease, fill .35s ease, stroke-width .2s ease; }
.radar-node.has-score .node-circle { fill: var(--pen-red); }
.radar-node .node-glow { transition: r .65s cubic-bezier(.2,.8,.2,1); }
.radar-node:hover .node-circle, .radar-node:focus .node-circle, .radar-node.is-selected .node-circle { stroke: var(--marker-teal); stroke-width: 3; }
.radar-node:focus .node-label { fill: var(--ink); font-weight: 700; }
.radar-node:hover .node-label { fill: var(--ink); font-weight: 700; }
.radar-node.is-winner .node-label { fill: var(--ink); font-weight: 700; }
.pen-circle { fill: none; stroke: var(--pen-red); stroke-width: 2.5; stroke-linecap: round; filter: url(#roughen); stroke-dasharray: 220; stroke-dashoffset: 220; transition: stroke-dashoffset .7s ease .15s; }
.pen-circle.is-drawn { stroke-dashoffset: 0; }
.pen-scratch { display: inline-block; letter-spacing: -3px; color: var(--pen-red); font-family: var(--mono); animation: scratch .65s steps(2, end) infinite; }
.pen-btn.is-thinking { box-shadow: 1px 1px 0 var(--ink); transform: translate(1px, 1px); }
.margin-notes-card[hidden], .template-card[hidden] { display: none; }
.margin-notes-card:not([hidden]), .template-card:not([hidden]) { animation: settle .4s ease both; }
@keyframes scratch { 50% { transform: translateX(3px) rotate(-2deg); opacity: .55; } }
@keyframes twinkle { 50% { transform: scale(1.2); opacity: .55; } }
@media (max-width: 540px) {
  .masthead-inner { padding: 14px 16px; gap: 14px; }
  .key-slot { width: 100%; flex-wrap: wrap; gap: 6px; }
  #apiKey { flex: 1; min-width: 140px; }
  .sheet { padding: 28px 12px 42px; gap: 24px; }
  .notebook, .radar-card { padding: 20px 14px 16px; }
  .radar-svg { width: calc(100% + 12px); margin-left: -6px; }
  .node-label { font-size: 10px; }
  .controls { align-items: stretch; }
  .pen-btn { justify-content: center; flex: 1; }
  .lang-toggle { flex: 1; }
  .sample-picker { width: 100%; justify-content: space-between; }
  .sample-picker select { flex: 1; max-width: none; }
  .lang-btn { flex: 1; padding-inline: 10px; }
  #problemInput { min-height: 175px; font-size: 16px; }
}