:root {
  --bg: #0f1729;
  --panel: #1f2b5e;
  --panel-2: #182447;
  --steel: #6a9bcc;
  --orange: #d97757;
  --teal: #00d4c8;
  --text: #e8ecf2;
  --muted: #8b9dc3;
  --soft: #c8d0e0;
  --line: rgba(232, 236, 242, 0.12);
  --radius: 10px;
  --shadow: 0 4px 24px rgba(0, 0, 0, 0.4);
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  font-size: 15px;
  line-height: 1.55;
  min-height: 100vh;
}

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

header.app-header {
  background: linear-gradient(135deg, #0f1729 0%, #1f2b5e 100%);
  padding: 22px 28px 18px;
  border-bottom: 1px solid var(--line);
}
header.app-header h1 {
  margin: 0 0 4px;
  font-size: 22px;
  letter-spacing: 0.01em;
}
header.app-header .subtitle {
  color: var(--muted);
  font-size: 13px;
}
header.app-header .post-link {
  font-size: 12px;
  color: var(--steel);
  margin-left: 8px;
}

nav.tab-strip {
  display: flex;
  gap: 4px;
  background: var(--panel-2);
  padding: 0 28px;
  border-bottom: 1px solid var(--line);
  overflow-x: auto;
}
nav.tab-strip button {
  background: none;
  border: none;
  color: var(--muted);
  padding: 14px 18px;
  font-size: 14px;
  font-weight: 500;
  cursor: pointer;
  border-bottom: 3px solid transparent;
  transition: color 0.15s, border-color 0.15s;
  font-family: inherit;
  white-space: nowrap;
}
nav.tab-strip button:hover { color: var(--text); }
nav.tab-strip button.active {
  color: var(--text);
  border-bottom-color: var(--orange);
}

main {
  max-width: 1240px;
  margin: 0 auto;
  padding: 28px;
}

.tab-pane { display: none; }
.tab-pane.active { display: block; }

h2 {
  font-size: 20px;
  margin: 0 0 14px;
  color: var(--text);
}
h3 {
  font-size: 16px;
  margin: 18px 0 8px;
  color: var(--steel);
}
p { margin: 0 0 12px; }

.lede {
  font-size: 16px;
  color: var(--muted);
  max-width: 780px;
}

.card {
  background: var(--panel-2);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 18px 20px;
  margin-bottom: 18px;
}
.card h3 { margin-top: 0; }

.grid {
  display: grid;
  gap: 18px;
}
.grid-2 { grid-template-columns: 1fr 1fr; }
.grid-3 { grid-template-columns: repeat(3, 1fr); }
.grid-main-side { grid-template-columns: 2fr 1fr; }

@media (max-width: 900px) {
  .grid-2, .grid-3, .grid-main-side { grid-template-columns: 1fr; }
}

.controls {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 18px;
  margin-bottom: 18px;
}
.control {
  background: var(--panel-2);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 12px 14px;
}
.control label {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  font-size: 12px;
  color: var(--muted);
  font-weight: 600;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  margin-bottom: 8px;
}
.control label .value {
  color: var(--teal);
  font-variant-numeric: tabular-nums;
  font-size: 14px;
  text-transform: none;
  letter-spacing: 0;
}
.control input[type="range"] {
  -webkit-appearance: none;
  appearance: none;
  width: 100%;
  height: 4px;
  background: rgba(232, 236, 242, 0.18);
  border-radius: 3px;
  outline: none;
}
.control input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 16px;
  height: 16px;
  background: var(--orange);
  border-radius: 50%;
  cursor: pointer;
  border: 2px solid var(--bg);
  box-shadow: 0 0 0 1px var(--orange);
}
.control input[type="range"]::-moz-range-thumb {
  width: 16px;
  height: 16px;
  background: var(--orange);
  border: 2px solid var(--bg);
  border-radius: 50%;
  cursor: pointer;
}
.control .hint {
  margin-top: 6px;
  color: var(--muted);
  font-size: 11px;
  line-height: 1.4;
}

.chart-area {
  position: relative;
  background: var(--panel-2);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 14px 16px 8px;
  margin-bottom: 18px;
}
.chart-area svg { width: 100%; height: auto; display: block; }
.chart-caption {
  font-size: 12px;
  color: var(--muted);
  padding-top: 6px;
  text-align: center;
}

.stat-row {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
  gap: 12px;
  margin-bottom: 12px;
}
.stat {
  background: var(--panel-2);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 12px 14px;
}
.stat .stat-label {
  font-size: 11px;
  color: var(--muted);
  letter-spacing: 0.05em;
  text-transform: uppercase;
  margin-bottom: 4px;
}
.stat .stat-value {
  font-size: 22px;
  font-weight: 600;
  font-variant-numeric: tabular-nums;
  color: var(--text);
}
.stat .stat-value.teal { color: var(--teal); }
.stat .stat-value.orange { color: var(--orange); }
.stat .stat-sub { font-size: 11px; color: var(--muted); margin-top: 2px; }

.pedagogy {
  background: rgba(106, 155, 204, 0.08);
  border-left: 3px solid var(--steel);
  border-radius: var(--radius);
  padding: 14px 18px;
}
.pedagogy h4 {
  margin: 0 0 8px;
  color: var(--steel);
  font-size: 13px;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}
.pedagogy ul { margin: 0; padding-left: 20px; }
.pedagogy li { margin-bottom: 6px; color: var(--text); font-size: 14px; }
.pedagogy li strong { color: var(--teal); }

button.action {
  background: var(--orange);
  color: #fff;
  border: none;
  border-radius: 8px;
  padding: 10px 18px;
  font-size: 13px;
  font-weight: 600;
  cursor: pointer;
  font-family: inherit;
  letter-spacing: 0.02em;
  transition: filter 0.15s, transform 0.15s;
}
button.action:hover { filter: brightness(1.1); }
button.action:active { transform: translateY(1px); }
button.action.secondary {
  background: rgba(255, 255, 255, 0.08);
  border: 1px solid var(--line);
  color: var(--text);
}
button.action[disabled] { opacity: 0.5; cursor: not-allowed; }

.tag {
  display: inline-block;
  font-size: 11px;
  padding: 2px 8px;
  border-radius: 10px;
  font-weight: 600;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}
.tag.rigorous { background: rgba(0, 212, 200, 0.18); color: var(--teal); }
.tag.cv       { background: rgba(217, 119, 87, 0.20); color: var(--orange); }

details.gloss {
  margin: 8px 0;
  background: rgba(255, 255, 255, 0.03);
  border-radius: 8px;
  padding: 8px 12px;
  border: 1px solid var(--line);
}
details.gloss[open] { background: rgba(0, 212, 200, 0.05); }
details.gloss summary {
  cursor: pointer;
  font-weight: 600;
  color: var(--text);
  font-size: 14px;
  list-style: none;
  display: flex;
  justify-content: space-between;
  align-items: center;
}
details.gloss summary::after {
  content: "▾";
  color: var(--muted);
  transition: transform 0.2s;
}
details.gloss[open] summary::after { transform: rotate(180deg); }
details.gloss .gloss-body {
  margin-top: 8px;
  font-size: 13px;
  color: var(--muted);
}
details.gloss .gloss-body em { color: var(--teal); font-style: normal; }

.cta-cards {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 14px;
  margin: 20px 0;
}
.cta-card {
  background: var(--panel-2);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 16px;
  cursor: pointer;
  transition: border-color 0.2s, transform 0.2s;
}
.cta-card:hover {
  border-color: var(--teal);
  transform: translateY(-2px);
}
.cta-card .cta-tag {
  font-size: 11px;
  color: var(--orange);
  font-weight: 700;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.tooltip {
  position: absolute;
  background: var(--panel);
  border: 1px solid var(--steel);
  border-radius: 6px;
  padding: 8px 10px;
  font-size: 12px;
  color: var(--text);
  pointer-events: none;
  opacity: 0;
  transition: opacity 0.15s;
  z-index: 1000;
  box-shadow: var(--shadow);
  max-width: 240px;
}
.tooltip.show { opacity: 1; }
.tooltip .tooltip-key { color: var(--muted); }
.tooltip .tooltip-val { color: var(--teal); font-variant-numeric: tabular-nums; }

.method-toggle {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}
.method-toggle label {
  background: rgba(255, 255, 255, 0.04);
  border: 1px solid var(--line);
  padding: 6px 12px;
  border-radius: 14px;
  font-size: 12px;
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  transition: all 0.15s;
}
.method-toggle input { accent-color: var(--orange); }
.method-toggle label:has(input:checked) {
  border-color: var(--orange);
  background: rgba(217, 119, 87, 0.10);
  color: var(--text);
}

.progress-bar {
  height: 6px;
  background: rgba(232, 236, 242, 0.12);
  border-radius: 3px;
  overflow: hidden;
  margin-top: 8px;
}
.progress-bar > div {
  height: 100%;
  background: linear-gradient(90deg, var(--steel), var(--teal));
  width: 0%;
  transition: width 0.05s linear;
}

.note {
  font-size: 12px;
  color: var(--muted);
  font-style: italic;
  margin-top: 8px;
}

.kbd {
  background: var(--panel);
  border: 1px solid var(--line);
  padding: 1px 6px;
  border-radius: 4px;
  font-family: ui-monospace, "SF Mono", Menlo, monospace;
  font-size: 12px;
  color: var(--teal);
}

footer.app-footer {
  border-top: 1px solid var(--line);
  padding: 18px 28px;
  font-size: 12px;
  color: var(--muted);
  text-align: center;
  margin-top: 40px;
}

.method-row {
  display: flex;
  justify-content: space-between;
  padding: 6px 0;
  border-bottom: 1px dashed var(--line);
}
.method-row:last-child { border-bottom: none; }
.method-row .label { color: var(--muted); }
.method-row .val { color: var(--text); font-variant-numeric: tabular-nums; font-weight: 600; }

/* ---- Tab strip: keyboard focus ---- */
nav.tab-strip button:focus-visible,
button.action:focus-visible,
.cta-card:focus-visible,
details.gloss summary:focus-visible,
.tab-pane:focus-visible {
  outline: 2px solid var(--teal);
  outline-offset: 2px;
}
.tab-pane:focus:not(:focus-visible) { outline: none; }

code {
  font-family: ui-monospace, "SF Mono", Menlo, monospace;
  font-size: 0.92em;
  color: var(--soft);
}

/* ---- Tab 1: animation chrome ---- */
.anim-head { margin: 10px 0 8px; }
.anim-title {
  color: var(--teal);
  font-weight: 600;
  font-size: 14px;
}
.anim-note {
  color: var(--soft);
  font-size: 13px;
  min-height: 2.6em;
}
.anim-controls {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}
.anim-controls button[aria-pressed="true"].secondary {
  border-color: var(--teal);
  color: var(--teal);
}

/* ---- CTA cards are links ---- */
a.cta-card, a.cta-card:hover { text-decoration: none; display: block; }
.cta-card .cta-title {
  display: block;
  margin: 6px 0;
  font-size: 15px;
  font-weight: 600;
  color: var(--text);
}
.cta-card .cta-text {
  display: block;
  font-size: 13px;
  color: var(--muted);
}
.cta-card .cta-tag { display: block; }

/* ---- Tab 2: OVB card ---- */
.subhead {
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.05em;
  text-transform: uppercase;
  color: var(--orange);
  margin-bottom: 4px;
}
.method-row { gap: 12px; }
.method-row .val { white-space: nowrap; }

/* ---- Tab 3: table view ---- */
details.table-card summary {
  cursor: pointer;
  font-weight: 600;
  color: var(--steel);
}
.table-wrap { overflow-x: auto; margin-top: 10px; }
.est-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 13px;
  font-variant-numeric: tabular-nums;
}
.est-table th, .est-table td {
  text-align: right;
  padding: 6px 8px;
  border-bottom: 1px solid var(--line);
  white-space: nowrap;
}
.est-table th:first-child, .est-table tbody th { text-align: left; font-weight: 500; color: var(--text); }
.est-table thead th { color: var(--muted); font-weight: 600; }

/* ---- Tab 5: quiz ---- */
.card.quiz h3 { font-size: 15px; }
.quiz-buttons {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin: 10px 0 4px;
}
.quiz-buttons button { text-align: left; }
.quiz-buttons button.picked-right { border-color: var(--teal); color: var(--teal); }
.quiz-buttons button.picked-wrong { border-color: var(--orange); color: var(--orange); }
.quiz-feedback {
  margin: 10px 0 0;
  font-size: 13px;
  line-height: 1.5;
}
.quiz-feedback.right { color: var(--teal); }
.quiz-feedback.wrong { color: var(--orange); }
.quiz-score {
  display: block;
  margin-top: 8px;
  font-size: 14px;
  color: var(--teal);
}

.load-error { border-color: var(--orange); color: var(--orange); }

/* Greek symbols must not be upper-cased by the label style. */
.control label .sym { text-transform: none; font-size: 14px; }

/* Estimator hats and residual tildes (β̂, γ̂, δ̂, x̃, ỹ). A combining accent
   (U+0302, U+0303) lands off-center in the system sans stack, so the accent is
   drawn by CSS, centered over the letter: <span class="hat">β</span>. Add "lo"
   for x-height letters (γ, x, y) so the accent sits closer. The span also
   blocks the upper-casing of .stat-label and similar labels. */
.hat, .tilde {
  position: relative;
  display: inline-block;
  line-height: 1;
  text-transform: none;
  letter-spacing: 0;
}
.hat::after, .tilde::after {
  position: absolute;
  left: 0;
  right: 0;
  text-align: center;
  line-height: 1;
  font-weight: 400;
  font-style: normal;
  pointer-events: none;
}
.hat::after      { content: "\02C6"; top: -0.36em; }
.tilde::after    { content: "\02DC"; top: -0.34em; }
.hat.lo::after   { top: -0.16em; }
.tilde.lo::after { top: -0.14em; }

/* ---- Phones ---- */
@media (max-width: 600px) {
  header.app-header { padding: 16px 16px 14px; }
  header.app-header h1 { font-size: 19px; }
  nav.tab-strip { padding: 0 8px; flex-wrap: wrap; overflow-x: visible; }
  nav.tab-strip button { padding: 10px 10px; font-size: 13px; }
  main { padding: 18px 16px; }
  .card { padding: 14px 14px; }
  .chart-area { padding: 10px 8px 6px; }
  .lede { font-size: 15px; }
  .method-row { flex-wrap: wrap; }
  .control input[type="range"] { height: 24px; background: transparent; }
  .control input[type="range"]::-webkit-slider-runnable-track { height: 4px; background: rgba(232, 236, 242, 0.18); border-radius: 3px; }
  .control input[type="range"]::-webkit-slider-thumb { width: 22px; height: 22px; margin-top: -9px; }
  button.action { min-height: 40px; }
  .est-table .ci { display: none; }
  .est-table tbody th { white-space: normal; }
}

@media (prefers-reduced-motion: reduce) {
  * { transition: none !important; }
}