/* Design system for Relatively Puzzled. Tokens first; every page reuses them.
   scripts/check_site.py reads the two token blocks below to check contrast. */

@font-face {
  font-family: "Newsreader";
  src: url("/fonts/newsreader-latin-wght-normal.woff2") format("woff2");
  font-weight: 200 800;
  font-style: normal;
  font-display: swap;
}
@font-face {
  font-family: "Newsreader";
  src: url("/fonts/newsreader-latin-wght-italic.woff2") format("woff2");
  font-weight: 200 800;
  font-style: italic;
  font-display: swap;
}
@font-face {
  font-family: "Instrument Sans";
  src: url("/fonts/instrument-sans-latin-wght-normal.woff2") format("woff2");
  font-weight: 400 700;
  font-style: normal;
  font-display: swap;
}

:root,
:root[data-theme="dark"] {
  --bg: #1d2523;
  --surface: #28322f;
  --tint: #303d37;
  --text: #f1efe5;
  --muted: #b8beb2;
  --accent: #cbd6a1;
  --accent-ink: #20291e;
  --rule: #49564c;
  --track-maths: #e3cf5c;
  --track-physics: #62c9c4;
  --correct: #78d08f;
  --retry: #f2908e;
  --state-ink: #14161a;
  color-scheme: dark;
}
:root[data-theme="light"] {
  --bg: #f7f5ed;
  --surface: #eeece2;
  --tint: #e5e9d9;
  --text: #242c26;
  --muted: #545e51;
  --accent: #3d562f;
  --accent-ink: #ffffff;
  --rule: #d0d1c3;
  --track-maths: #645b2b;
  --track-physics: #355b4d;
  --correct: #19702f;
  --retry: #a9302e;
  --state-ink: #ffffff;
  color-scheme: light;
}

:root {
  --serif: "Newsreader", Georgia, "Times New Roman", serif;
  --sans: "Instrument Sans", system-ui, -apple-system, "Segoe UI", sans-serif;
  --space-1: .5rem;
  --space-2: 1rem;
  --space-3: 1.5rem;
  --space-4: 2.5rem;
  --space-5: 4rem;
  --radius: 4px;
  --radius-lg: 14px;
  --measure: 40rem;
}

*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font: 1.125rem/1.65 var(--serif);
  overflow-wrap: break-word;
}
img, svg, iframe { max-width: 100%; }
a { color: var(--accent); text-underline-offset: .18em; }
a:hover { text-decoration-thickness: 2px; }
:focus-visible { outline: 3px solid var(--accent); outline-offset: 3px; border-radius: var(--radius); }

.wrap { width: min(100% - 2 * var(--space-3), 68rem); margin-inline: auto; }
.skip { position: absolute; left: var(--space-2); top: -4rem; background: var(--accent); color: var(--accent-ink); padding: .5rem 1rem; z-index: 10; font-family: var(--sans); }
.skip:focus { top: var(--space-1); }

h1, h2, h3 { font-family: var(--serif); font-weight: 400; line-height: 1.12; letter-spacing: -.012em; margin: 0 0 var(--space-2); text-wrap: balance; }
h1 { font-size: clamp(2.5rem, 6.4vw, 4.4rem); letter-spacing: -.022em; }
h2 { font-size: clamp(1.7rem, 3.4vw, 2.3rem); }
h3 { font-size: 1.3rem; }
p { margin: 0 0 var(--space-2); }
.lead { font-size: 1.3rem; line-height: 1.55; color: var(--text); max-width: 34rem; }
.note { color: var(--muted); font-size: 1rem; max-width: 36rem; }

/* header and footer */
.site-header { border-bottom: 1px solid var(--rule); font-family: var(--sans); }
.bar { display: flex; align-items: center; justify-content: space-between; gap: var(--space-2); min-height: 4rem; flex-wrap: wrap; padding-block: .5rem; }
.wordmark { font: 500 1.25rem/1 var(--serif); color: var(--text); text-decoration: none; letter-spacing: -.01em; }
.site-header nav { display: flex; align-items: center; gap: var(--space-3); font-size: .95rem; }
.site-header nav a { color: var(--text); text-decoration: none; }
.site-header nav a:hover { color: var(--accent); }
.theme-toggle { display: inline-grid; place-items: center; width: 2.5rem; height: 2.5rem; padding: 0; border: 1px solid var(--rule); border-radius: var(--radius); background: transparent; color: var(--text); cursor: pointer; }
.theme-toggle:hover { border-color: var(--accent); color: var(--accent); }
.theme-toggle .lucide { width: 1.2rem; height: 1.2rem; }
.theme-toggle .to-dark { display: none; }
:root[data-theme="light"] .theme-toggle .to-light { display: none; }
:root[data-theme="light"] .theme-toggle .to-dark { display: inline; }
.site-footer { margin-top: var(--space-5); padding-block: var(--space-4); border-top: 1px solid var(--rule); color: var(--muted); font: .95rem/1.6 var(--sans); }
.site-footer p { margin-bottom: .5rem; }

.lucide { width: 1.1em; height: 1.1em; flex: none; vertical-align: -.17em; }
.text-link .lucide, .site-footer .lucide, .about .lucide { margin-right: .4em; }

/* buttons */
.actions { display: flex; flex-wrap: wrap; align-items: center; gap: var(--space-2) var(--space-3); margin-top: var(--space-3); font-family: var(--sans); }
.button { display: inline-block; background: var(--accent); color: var(--accent-ink); font-weight: 600; text-decoration: none; padding: .8rem 1.35rem; border-radius: var(--radius); }
.button:hover { text-decoration: underline; text-decoration-thickness: 2px; }
.text-link { font-weight: 500; text-decoration: none; }
.text-link:hover { text-decoration: underline; }

/* landing page */
.hero { display: grid; grid-template-columns: minmax(0, 1.05fr) minmax(0, 1fr); gap: var(--space-4); align-items: center; padding-block: var(--space-5) var(--space-4); }
.hero-figure { margin: 0; }
.hero-figure svg { display: block; width: 100%; height: auto; }
.hero-figure figcaption { margin-top: var(--space-1); color: var(--muted); font: .9rem/1.5 var(--sans); max-width: 26rem; }
.orbit { fill: none; stroke: var(--muted); opacity: .55; stroke-width: 2; stroke-dasharray: 1; stroke-dashoffset: 0; }
.star { fill: var(--accent); }
.planet { fill: var(--text); }
.vector { stroke: var(--accent); stroke-width: 3; stroke-linecap: round; }
.head { fill: var(--accent); }
.hero-figure text { fill: var(--accent); font: italic 22px var(--serif); }
.series, .how, .about { padding-block: var(--space-4); }
.series h2, .how h2, .about h2 { font-size: 1.5rem; color: var(--muted); font-weight: 400; }

.series-row { display: grid; grid-template-columns: minmax(0, 1.2fr) minmax(0, 1.6fr) auto; gap: var(--space-2) var(--space-4); align-items: baseline; padding: var(--space-3) var(--space-3); background: var(--tint); border-radius: var(--radius); color: var(--text); text-decoration: none; }
.series-row:hover .series-go { text-decoration: underline; }
.series-title { font-size: 1.7rem; line-height: 1.15; }
.series-text { color: var(--muted); }
.series-go { font: 600 1rem var(--sans); color: var(--accent); white-space: nowrap; }
.series-go .lucide { margin-left: .4em; }
.series .note { margin-top: var(--space-2); }

.steps { list-style: none; counter-reset: step; display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: var(--space-4); margin: 0 0 var(--space-2); padding: 0; }
.steps li { counter-increment: step; padding-top: var(--space-2); border-top: 1px solid var(--rule); }
.steps .lucide { width: 1.6rem; height: 1.6rem; color: var(--accent); display: block; margin-bottom: var(--space-1); }
.steps h3::before { content: counter(step) ". "; color: var(--muted); }
.steps p { color: var(--muted); }
.about p { max-width: var(--measure); }

.page-not-found { padding-block: var(--space-5); }

/* orbit draws itself once on load; reduced motion shows it finished */
@media (prefers-reduced-motion: no-preference) {
  .orbit { animation: draw 2.6s cubic-bezier(.4, .1, .2, 1) 0.2s backwards; }
  .after { animation: reveal .6s ease 2.4s backwards; }
  @keyframes draw { from { stroke-dashoffset: 1; } }
  @keyframes reveal { from { opacity: 0; } }
}

/* reading pages (Chapters and utility pages) until the Lesson stepper arrives */
.prose-page main { width: min(100% - 2 * var(--space-3), var(--measure)); margin: var(--space-4) auto 0; }
/* prose rules apply to reading pages only, never the landing or 404 pages */
.prose-page main h1 .code { color: var(--accent); margin-right: .4em; }
.prose-page main h2, .prose-page main h3 { margin-top: var(--space-4); }
main .table-wrap { overflow-x: auto; max-width: 100%; }
main table { border-collapse: collapse; font: .95rem/1.5 var(--sans); }
main th, main td { border-bottom: 1px solid var(--rule); padding: .4rem .8rem; text-align: left; }
.prose-page main code { font-size: .9em; background: var(--surface); padding: .1em .3em; border-radius: var(--radius); }
.prose-page main pre { overflow-x: auto; background: var(--surface); padding: var(--space-2); border-radius: var(--radius); }
.admonition, details { background: var(--tint); border-radius: var(--radius); padding: .6rem var(--space-2); margin: var(--space-2) 0; }
.admonition-title, summary { font: 600 .95rem var(--sans); }
.admonition-title { display: inline-block; margin: 0 0 .4rem; padding: .1rem .6rem; border-radius: 999px; background: var(--accent); color: var(--accent-ink); font-size: .8rem; letter-spacing: .05em; text-transform: uppercase; }
.admonition > :last-child, details > :last-child { margin-bottom: 0; }
figure.diagram { margin: var(--space-3) 0; }
.diagram svg { display: block; width: 100%; max-width: 34rem; height: auto; margin-inline: auto; }
.diagram figcaption { max-width: 34rem; margin: .6rem auto 0; font: .85rem/1.5 var(--sans); color: var(--muted); }
.diagram .ln, .diagram .vec, .diagram .guide, .diagram .body, .diagram .soft { fill: none; stroke: var(--text); stroke-width: 2; stroke-linecap: round; stroke-linejoin: round; }
.diagram .vec { stroke: var(--accent); stroke-width: 3.5; }
.diagram .guide { stroke-width: 1.2; stroke-dasharray: 5 4; opacity: .6; }
.diagram .body { fill: var(--surface); }
.diagram .soft { stroke: var(--rule); }
.diagram .dot { fill: var(--text); }
.diagram .dot-a, .diagram .head { fill: var(--accent); }
.diagram .t, .diagram .tm { fill: var(--text); font: 600 15px var(--sans); }
.diagram .tm { font: italic 16px var(--serif); }
.diagram .ta { fill: var(--accent); font: italic 600 16px var(--serif); }
.diagram .tn { fill: var(--accent); font: 600 14px var(--sans); }
.diagram .ts { fill: var(--muted); font: 500 12.5px var(--sans); }
.diagram .mid { text-anchor: middle; }
.diagram .end { text-anchor: end; }

/* phones */
@media (max-width: 52rem) {
  .hero { grid-template-columns: 1fr; padding-block: var(--space-4); }
  .series-row { grid-template-columns: 1fr; }
  .steps { grid-template-columns: 1fr; gap: var(--space-3); }
}

/* series page: roadmap of Chapters */
.series-hero { padding-block: var(--space-5) var(--space-3); }
.series-hero .lead { max-width: 40rem; }
.key-numbers { display: flex; flex-wrap: wrap; gap: var(--space-2) var(--space-4); margin: var(--space-3) 0; padding: 0; font-family: var(--sans); }
.key-numbers div { display: flex; flex-direction: column; min-width: 7rem; }
.key-numbers dt { color: var(--muted); font-size: .9rem; order: 2; }
.key-numbers dd { margin: 0; font: 400 2.2rem/1.1 var(--serif); }
.how-short { display: flex; flex-wrap: wrap; gap: var(--space-1) var(--space-3); list-style: none; margin: 0 0 var(--space-2); padding: 0; counter-reset: how; font-family: var(--sans); color: var(--muted); }
.how-short li { counter-increment: how; }
.how-short li::before { content: counter(how) ". "; }
.roadmap-section { padding-block: var(--space-3) 0; }
.roadmap-section h2, .later h2 { font-size: 1.5rem; }
.progress-panel { display: flex; flex-wrap: wrap; align-items: center; gap: var(--space-1) var(--space-3); margin: var(--space-2) 0; padding: var(--space-2); background: var(--surface); border-radius: var(--radius); font-family: var(--sans); }
.progress-panel[hidden], .chapter-card[hidden], .card-progress[hidden], #resume[hidden], .later[hidden] { display: none; }
.progress-panel progress { flex: 1 1 14rem; height: .6rem; accent-color: var(--accent); }
.progress-text { margin: 0; color: var(--muted); font-size: .95rem; }
.progress-panel .button { padding: .5rem 1rem; margin: 0; }
.filters { display: flex; flex-wrap: wrap; gap: var(--space-1); margin: var(--space-2) 0 var(--space-1); font-family: var(--sans); }
.filters button { padding: .45rem 1rem; border: 1px solid var(--rule); border-radius: 999px; background: transparent; color: var(--text); font: 500 .95rem var(--sans); cursor: pointer; }
.filters button:hover { border-color: var(--accent); }
.filters button[aria-pressed="true"] { background: var(--accent); border-color: var(--accent); color: var(--accent-ink); }
#filter-count { color: var(--muted); font: .9rem var(--sans); margin-bottom: var(--space-2); }
.roadmap { list-style: none; margin: 0; padding: 0 0 0 var(--space-3); border-left: 2px solid var(--rule); }
.chapter-card { position: relative; margin: 0 0 var(--space-2); padding: var(--space-2) var(--space-3); background: var(--surface); border-radius: var(--radius); }
.chapter-card::before { content: ""; position: absolute; left: calc(-1 * var(--space-3) - 7px); top: 1.6rem; width: 12px; height: 12px; border-radius: 50%; background: var(--track); border: 2px solid var(--bg); }
.chapter-card[data-track="maths"] { --track: var(--track-maths); }
.chapter-card[data-track="physics"] { --track: var(--track-physics); }
.chapter-card[data-status="planned"] { opacity: .6; }
.card-head { display: flex; flex-wrap: wrap; gap: var(--space-1) var(--space-2); align-items: baseline; font: 600 .85rem var(--sans); letter-spacing: .04em; text-transform: uppercase; }
.card-code, .card-track { padding: .05rem .55rem; border: 1px solid var(--track); border-radius: 999px; color: var(--track); }
.card-code::before { content: ""; display: inline-block; width: .6em; height: .6em; margin-right: .4em; border-radius: 50%; background: var(--track); }
.card-status { margin-left: auto; color: var(--muted); letter-spacing: 0; text-transform: none; font-weight: 500; }
.chapter-card h3 { margin: .3rem 0; font-size: 1.4rem; }
.chapter-card h3 a { color: var(--text); text-decoration: none; }
.chapter-card h3 a::after { content: ""; position: absolute; inset: 0; }
.chapter-card h3 a:hover { text-decoration: underline; }
.card-goal { margin: 0 0 var(--space-1); color: var(--muted); font-size: 1rem; }
.chips { display: flex; flex-wrap: wrap; align-items: center; gap: .35rem; list-style: none; margin: 0; padding: 0; font: .85rem var(--sans); color: var(--muted); }
.chips li { padding: .1rem .55rem; border: 1px solid var(--rule); border-radius: 999px; }
.chips li.chips-label { border: 0; padding-left: 0; }
.card-progress { margin: var(--space-1) 0 0; font: 600 .9rem var(--sans); color: var(--accent); }
.later { padding-block: var(--space-4) 0; }
.later ol { list-style: none; margin: 0; padding: 0; opacity: .6; font-family: var(--sans); }
.later li { padding: var(--space-1) 0; border-top: 1px solid var(--rule); }
.later li span { color: var(--muted); margin-left: .5em; }
.video-part { margin: var(--space-3) 0; }

.link-button { padding: 0; border: 0; background: none; color: var(--accent); font: 500 1rem var(--sans); cursor: pointer; }
.link-button:hover { text-decoration: underline; }
.not-found-heading { margin-top: var(--space-4); font-size: 1.5rem; color: var(--muted); }
.not-found-list { list-style: none; margin: 0; padding: 0; display: grid; grid-template-columns: repeat(auto-fill, minmax(min(100%, 16rem), 1fr)); gap: var(--space-1) var(--space-3); font-family: var(--sans); }
.not-found-list .card-code { color: var(--muted); font-weight: 600; margin-right: .3em; }