/* IntroStatsCalc styles
   Colors come from the approved mockup. Every text/background pair meets WCAG 2.1 AA
   (4.5:1 for text; 3:1 for input borders, focus rings and graph marks). */
:root {
  --bg: #F6F5F1;
  --card: #FFFFFF;
  --border: #E4E1D8;
  --input-border: #7D796F;   /* darkened from the mockup's #CFCBBF for 3:1 contrast */
  --text: #1A1D21;
  --text-2: #3E4248;
  --text-3: #5B5F66;
  --accent: #1D5F7A;
  --accent-strong: #154A60;
  --accent-tint: #E8F0F3;
  --shade: rgba(29, 95, 122, 0.22);
  --warn-bg: #FDF3E7;
  --warn-text: #7A4510;
  --error-bg: #FBECEC;
  --error-text: #9B1C1C;
  --radius: 14px;
  --serif: "Source Serif 4", Georgia, serif;
  --sans: "IBM Plex Sans", system-ui, -apple-system, "Segoe UI", sans-serif;
  --mono: "IBM Plex Mono", ui-monospace, Consolas, monospace;
}

* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body { margin: 0; background: var(--bg); color: var(--text); font: 400 1rem/1.6 var(--sans); }
.wrap { max-width: 1120px; margin: 0 auto; padding: 0 16px; }
a { color: var(--accent); }
a:hover { color: var(--accent-strong); }
sub, sup { line-height: 0; }

/* ---------- accessibility helpers ---------- */
.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; }
.skip-link { position: absolute; left: -9999px; top: 8px; background: var(--accent); color: #fff; padding: 8px 14px; border-radius: 8px; z-index: 10; text-decoration: none; font-weight: 600; }
.skip-link:focus { left: 16px; color: #fff; }
:focus-visible { outline: 3px solid var(--accent); outline-offset: 2px; }
[hidden] { display: none !important; }

/* ---------- header + tabs ---------- */
.site-header { background: var(--card); border-bottom: 1px solid var(--border); }
.header-row { display: flex; align-items: center; justify-content: space-between; min-height: 60px; gap: 12px; }
.brand { display: inline-flex; align-items: center; gap: 10px; color: var(--text); text-decoration: none; }
.brand-mark { display: inline-grid; place-items: center; width: 34px; height: 34px; border-radius: 9px; background: var(--accent); color: #fff; font: 500 1.15rem/1 var(--mono); }
.brand-name { font: 700 1.3rem/1 var(--serif); letter-spacing: -0.01em; }
.edition { font-size: 0.8rem; font-weight: 600; color: var(--accent); background: var(--accent-tint); border-radius: 999px; padding: 4px 12px; white-space: nowrap; }
.tabs ul { list-style: none; margin: 0; padding: 0; display: flex; gap: 4px; overflow-x: auto; scrollbar-width: thin; }
.tabs a { display: block; white-space: nowrap; text-decoration: none; color: var(--text-2); padding: 8px 12px; border-radius: 8px; font-weight: 500; font-size: 0.95rem; }
.tabs a:hover { background: var(--bg); color: var(--text); }
.grouptabs { padding-bottom: 6px !important; }
.grouptabs a.active { background: var(--accent-tint); color: var(--accent-strong); font-weight: 600; }
.subtabs { border-top: 1px solid var(--border); padding: 6px 0 8px !important; }
.subtabs a { font-size: 0.9rem; padding: 6px 10px; }
.subtabs a.active { color: var(--accent-strong); box-shadow: inset 0 -2px 0 var(--accent); border-radius: 8px 8px 0 0; font-weight: 600; }

/* ---------- page head ---------- */
main { padding-bottom: 40px; }
.page-head { padding: 28px 0 18px; max-width: 820px; }
h1 { font: 700 clamp(1.7rem, 4vw, 2.4rem)/1.15 var(--serif); margin: 0 0 8px; letter-spacing: -0.015em; }
.lede { font-size: 1.1rem; color: var(--text-2); margin: 0; }
.module-tag { display: inline-block; vertical-align: middle; margin-left: 10px; font: 600 0.75rem/1 var(--sans); letter-spacing: 0.02em; color: var(--accent-strong); background: var(--accent-tint); border-radius: 999px; padding: 5px 10px; }
.hero { padding: 48px 0 16px; max-width: 780px; }
.hero h1 { font-size: clamp(2rem, 5vw, 3rem); }
.class-note { margin-top: 18px; padding: 12px 16px; border-left: 4px solid var(--accent); background: var(--accent-tint); border-radius: 0 10px 10px 0; color: var(--text-2); }
.class-note .module-tag { margin-left: 0; }

/* ---------- cards ---------- */
.card { background: var(--card); border: 1px solid var(--border); border-radius: var(--radius); padding: 20px; }
.card-title { font: 600 1.05rem/1.3 var(--sans); margin: 0 0 12px; }
h2 { font: 600 1.35rem/1.25 var(--serif); }
h3 { font: 600 1rem/1.3 var(--sans); }

/* ---------- calculator layout ---------- */
.calc-layout { display: grid; grid-template-columns: 340px minmax(0, 1fr); gap: 20px; align-items: start; }
.inputs { position: sticky; top: 12px; }
.results { display: grid; gap: 16px; min-width: 0; }
#results { display: grid; gap: 16px; min-width: 0; }
#results > * { min-width: 0; }
.explainer { margin-top: 24px; }
.explainer h2 { font-size: 1.2rem; margin: 18px 0 6px; }
.explainer h2:first-of-type { margin-top: 0; }
.explainer p, .explainer li { color: var(--text-2); max-width: 75ch; }
.related { border-top: 1px solid var(--border); padding-top: 12px; margin-top: 18px; font-size: 0.95rem; }

/* ---------- form controls ---------- */
form { display: grid; gap: 14px; }
.field { display: grid; gap: 4px; min-width: 0; }
.field label, .choice legend { font-weight: 600; font-size: 0.92rem; color: var(--text); }
.field input[type=text], .field textarea, .field select {
  width: 100%; font: 400 1rem/1.4 var(--mono); color: var(--text); background: #fff;
  border: 1px solid var(--input-border); border-radius: 8px; padding: 8px 10px;
}
.field textarea { resize: vertical; min-height: 3.2em; }
.field input:focus, .field textarea:focus, .field select:focus { outline: 3px solid var(--accent); outline-offset: 0; border-color: var(--accent); }
.hint { margin: 0; font-size: 0.82rem; color: var(--text-3); line-height: 1.4; }
.row { display: grid; grid-template-columns: repeat(auto-fit, minmax(90px, 1fr)); gap: 10px; align-items: end; }
.row:empty { display: none; }
.group { display: grid; gap: 8px; }
.group-title { margin: 0; font-size: 0.85rem; text-transform: uppercase; letter-spacing: 0.06em; color: var(--text-3); }
.check { grid-template-columns: auto 1fr; align-items: start; gap: 8px; }
.check input { width: 18px; height: 18px; margin: 3px 0 0; accent-color: var(--accent); }
.check label { font-weight: 500; }

/* segmented radio buttons */
.choice { border: 0; margin: 0; padding: 0; min-width: 0; }
.choice legend { padding: 0; margin-bottom: 6px; }
.seg { display: grid; grid-template-columns: repeat(var(--cols, 2), minmax(0, 1fr)); gap: 6px; }
.seg input { position: absolute; opacity: 0; width: 1px; height: 1px; }
.seg label {
  display: flex; align-items: center; justify-content: center; text-align: center; min-height: 40px;
  padding: 6px 8px; border: 1px solid var(--input-border); border-radius: 8px; background: #fff;
  font-size: 0.88rem; font-weight: 500; color: var(--text-2); cursor: pointer; line-height: 1.25;
}
.seg label:hover { border-color: var(--accent); color: var(--text); }
.seg input:checked + label { background: var(--accent-tint); border-color: var(--accent); color: var(--accent-strong); font-weight: 600; box-shadow: inset 0 0 0 1px var(--accent); }
.seg input:focus-visible + label { outline: 3px solid var(--accent); outline-offset: 2px; }

.btn { font: 600 0.95rem/1 var(--sans); background: var(--accent); color: #fff; border: 0; border-radius: 8px; padding: 11px 16px; cursor: pointer; }
.btn:hover { background: var(--accent-strong); }
.btn-quiet { background: transparent; color: var(--accent); border: 1px solid var(--input-border); }
.btn-quiet:hover { background: var(--accent-tint); color: var(--accent-strong); }
.updates { margin: 0; font-size: 0.82rem; color: var(--text-3); }
.form-actions { display: flex; gap: 8px; }

/* ---------- results ---------- */
.answer-card { background: var(--card); border: 1px solid var(--border); border-left: 5px solid var(--accent); border-radius: var(--radius); padding: 18px 20px; }
.answer-main { margin: 0 0 6px; font: 500 clamp(1.25rem, 3vw, 1.65rem)/1.3 var(--mono); color: var(--text); overflow-wrap: anywhere; }
.answer-sentence { margin: 0; color: var(--text-2); font-size: 1.05rem; }
.answer-card.error { border-left-color: var(--error-text); background: var(--error-bg); }
.answer-card.error .answer-main { font-family: var(--sans); font-weight: 600; color: var(--error-text); font-size: 1.15rem; }
.note-card { margin: 0; padding: 12px 16px; background: var(--warn-bg); color: var(--warn-text); border-radius: 10px; font-size: 0.95rem; }
.figure-card { background: var(--card); border: 1px solid var(--border); border-radius: var(--radius); padding: 12px 8px 4px; }
.fig { width: 100%; height: auto; display: block; }
.fig .curve { fill: none; stroke: var(--text); stroke-width: 2; }
.fig .shade { fill: var(--shade); stroke: none; }
.fig .axis, .fig .tick { stroke: var(--text-3); stroke-width: 1.2; }
.fig .grid { stroke: var(--border); stroke-width: 1; }
.fig .ticklabel { font: 400 12px var(--mono); fill: var(--text-2); }
.fig .axislabel { font: 500 13px var(--sans); fill: var(--text-2); }
.fig .mark { stroke: var(--accent-strong); stroke-width: 2; }
.fig .mark.dashed { stroke: #8A4B12; stroke-dasharray: 5 4; stroke-width: 1.6; }
.fig .marklabel { font: 500 12px var(--mono); fill: var(--text); paint-order: stroke; stroke: #fff; stroke-width: 4px; stroke-linejoin: round; }
.fig .bar { fill: #C9D9E0; stroke: var(--accent); stroke-width: 0.6; }
.fig .bar.hit { fill: var(--accent); }
.fig .box { fill: var(--accent-tint); stroke: var(--accent-strong); stroke-width: 2; }
.fig .median { stroke: var(--accent-strong); stroke-width: 3; }
.fig .whisker { stroke: var(--text-2); stroke-width: 2; }
.fig .outlier { fill: var(--text); }
.fig .point { fill: var(--accent); fill-opacity: 0.85; stroke: #fff; stroke-width: 1; }
.fig .fitline { stroke: #8A4B12; stroke-width: 2.2; }

.kv { width: 100%; border-collapse: collapse; font-size: 0.95rem; }
.kv th { text-align: left; font-weight: 500; color: var(--text-2); padding: 7px 10px 7px 0; border-bottom: 1px solid var(--border); }
.kv td { text-align: right; font-family: var(--mono); padding: 7px 0; border-bottom: 1px solid var(--border); overflow-wrap: anywhere; }
.kv tr:last-child th, .kv tr:last-child td { border-bottom: 0; }

.table-scroll { overflow-x: auto; }
.data { width: 100%; border-collapse: collapse; font-size: 0.92rem; }
.data caption { text-align: left; font-weight: 600; padding-bottom: 8px; }
.data th, .data td { padding: 7px 10px; border-bottom: 1px solid var(--border); text-align: right; white-space: nowrap; }
.data thead th { background: var(--bg); font-weight: 600; color: var(--text); }
.data tbody th { text-align: left; font-weight: 500; }
.data td { font-family: var(--mono); }
.data .exp { color: var(--text-3); font-size: 0.85em; }

.ti-card .ti-menu { margin: 0 0 6px; color: var(--text-2); font-size: 0.95rem; }
.ti-cmd { display: inline-block; font: 500 0.95rem/1.5 var(--mono); background: #1F2328; color: #F2F2EE; padding: 6px 10px; border-radius: 6px; overflow-wrap: anywhere; }
.ti-card p + .ti-menu { margin-top: 12px; }

.steps-card summary { font-weight: 600; cursor: pointer; font-size: 1.05rem; }
.steps-card summary:hover { color: var(--accent-strong); }
.steps { margin: 12px 0 0; padding-left: 22px; display: grid; gap: 10px; color: var(--text-2); }
.steps li { overflow-wrap: anywhere; }

.ad-slot { margin-top: 16px; min-height: 250px; }

/* ---------- home ---------- */
.home-group { margin: 28px 0; }
.home-group h2 { margin: 0 0 2px; }
.group-blurb { margin: 0 0 12px; color: var(--text-3); }
.tool-grid { list-style: none; margin: 0; padding: 0; display: grid; grid-template-columns: repeat(auto-fill, minmax(260px, 1fr)); gap: 12px; }
.tool { display: grid; gap: 4px; height: 100%; padding: 14px 16px; background: var(--card); border: 1px solid var(--border); border-radius: 12px; text-decoration: none; color: var(--text); }
.tool:hover { border-color: var(--accent); box-shadow: 0 2px 10px rgba(29, 95, 122, 0.08); color: var(--text); }
.tool-name { font-weight: 600; }
.tool-name .module-tag { margin-left: 8px; }
.tool-desc { font-size: 0.9rem; color: var(--text-3); }

/* ---------- prose pages ---------- */
.prose { max-width: 820px; margin-top: 18px; }
.prose h2 { font-size: 1.25rem; margin: 18px 0 6px; }
.prose h2:first-child { margin-top: 0; }
.prose p, .prose li { color: var(--text-2); }
main > h1 { margin-top: 32px; }

/* ---------- footer ---------- */
.site-footer { border-top: 1px solid var(--border); background: var(--card); padding: 24px 0 16px; color: var(--text-3); font-size: 0.9rem; }
.footer-grid { display: flex; flex-wrap: wrap; justify-content: space-between; gap: 16px; }
.footer-grid p { margin: 0 0 6px; max-width: 520px; }
.footer-brand { font: 700 1.05rem var(--serif); color: var(--text) !important; }
.footer-links { list-style: none; margin: 0; padding: 0; display: flex; gap: 18px; flex-wrap: wrap; }
.fineprint { margin-top: 12px; font-size: 0.82rem; }
.fineprint p { margin: 0; }

/* ---------- small screens ---------- */
@media (max-width: 860px) {
  .calc-layout { grid-template-columns: minmax(0, 1fr); }
  .inputs { position: static; }
}
@media (max-width: 600px) {
  .fig .ticklabel, .fig .marklabel { font-size: 21px; }
  .fig .axislabel { font-size: 22px; }
  .fig .curve { stroke-width: 3; }
}
@media (prefers-reduced-motion: reduce) { * { animation: none !important; transition: none !important; } }