/* ==========================================================================
   site.css — the public pages (home, catalogue, sign-in).
   "Colour chapters": every section is a flat field of one course colour,
   floor to ceiling, on one 12-column grid with one pair of margins.
   Colours and faces come from tokens.css. The course reader uses style.css.
   ========================================================================== */

:root {
  --m: clamp(16px, 2.2vw, 32px);           /* the one pair of outer margins */
  --gap: clamp(16px, 2.2vw, 32px);
  --s-small: clamp(0.8125rem, 0.79rem + 0.1vw, 0.875rem);
  --s-body: clamp(1.0625rem, 1rem + 0.25vw, 1.1875rem);
  --s-lead: clamp(1.25rem, 1.1rem + 0.7vw, 1.625rem);
  --s-head: clamp(2rem, 1.3rem + 2.8vw, 3.5rem);
  --s-display: clamp(2.75rem, 8.4vw, 8.25rem);
  --ease-out: cubic-bezier(.16, 1, .3, 1);
  --f: var(--bg); --fi: var(--text);       /* current field and its ink */
}

* { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }
body {
  background: var(--bg); color: var(--text);
  font-family: var(--sans); font-size: var(--s-body); line-height: 1.5;
  overflow-x: hidden;
}
::selection { background: var(--field-rag); color: #1a1a1a; }
img { display: block; max-width: 100%; height: auto; }
a { color: inherit; }
:focus-visible { outline: 3px solid currentColor; outline-offset: 3px; }

h1, h2, .display {
  font-family: var(--display); font-weight: 700;
  letter-spacing: -0.04em; line-height: 0.88;
  text-wrap: balance;
}
h3 { font-size: var(--s-body); font-weight: 600; line-height: 1.3; }
code { font-family: var(--mono); font-size: .9em; }

/* ---------- Fields: one flat colour each, with its own ink ---------- */
[data-field] { background: var(--f); color: var(--fi); }
[data-field="db"]   { --f: var(--field-db);  --fi: var(--field-db-ink); }
[data-field="rag"]  { --f: var(--field-rag); --fi: var(--field-rag-ink); }
[data-field="llm"],
[data-field="black"] { --f: var(--field-llm); --fi: var(--field-llm-ink); }
[data-field="dsa"]  { --f: var(--field-dsa); --fi: var(--field-dsa-ink); }
[data-field="bone"] { --f: var(--bg);        --fi: var(--text); }
[data-field="surface"] { --f: var(--bg-3);   --fi: var(--text); }
[data-field="accent"]  { --f: var(--accent); --fi: var(--accent-ink); }

.field {
  min-height: 90svh;
  padding: clamp(96px, 11vw, 176px) var(--m);
}

/* ---------- Buttons: one shape (pill), flat, in the field's ink ---------- */
.btn {
  display: inline-flex; align-items: center; gap: .6em;
  font: 600 var(--s-body)/1 var(--sans);
  padding: .95em 1.6em;
  border: 0; border-radius: 999px; cursor: pointer;
  text-decoration: none;
  background: var(--fi); color: var(--f);
  transition: transform .2s var(--ease-out), opacity .2s;
}
.btn:hover { opacity: .86; }
.btn:active { transform: scale(.96); }
.btn.primary { background: var(--accent); color: var(--accent-ink); }

.link {
  color: inherit; font-weight: 600;
  text-decoration: underline; text-decoration-thickness: 2px;
  text-underline-offset: .22em;
  transition: text-underline-offset .2s var(--ease-out);
}
.link:hover { text-underline-offset: .38em; }

.theme-toggle {
  font: 600 var(--s-small)/1 var(--sans);
  height: 44px; padding: 0 12px; border-radius: 999px; border: 0; cursor: pointer;
  background: transparent; color: inherit;
  text-decoration: underline 2px transparent; text-underline-offset: .3em;
  transition: text-decoration-color .2s, transform .2s var(--ease-out);
}
.theme-toggle:hover { text-decoration-color: currentColor; }
.theme-toggle:active { transform: scale(.94); }

.wordmark {
  font-family: var(--display); font-weight: 700; letter-spacing: -0.03em;
  font-size: var(--s-lead); line-height: 1; text-decoration: none; color: inherit;
}

/* ---------- The bar: wordmark, a few links, one action. Takes the
   colours of the field beneath it (the page's signature move). ---------- */
.bar {
  position: fixed; inset: 0 0 auto 0; z-index: 30;
  height: 60px; padding: 0 var(--m);
  display: flex; align-items: center; gap: clamp(14px, 2vw, 28px);
  background: var(--f); color: var(--fi);
  transition: background-color .3s ease, color .3s ease, transform .45s var(--ease-out);
}
.bar.away { transform: translateY(-100%); }
.bar .wordmark { margin-right: auto; }
.bar a:not(.wordmark) { font-size: var(--s-small); font-weight: 600; text-decoration: none; }
.bar a:not(.wordmark):hover { text-decoration: underline; text-underline-offset: .3em; }
@media (max-width: 720px) { .bar .wide { display: none; } }

/* ---------- Entrances: parts of a section arrive in reading order ---------- */
html.js [data-rise] {
  opacity: 0; transform: translateY(28px);
  transition: opacity .8s var(--ease-out), transform .8s var(--ease-out);
  transition-delay: calc(var(--i, 0) * 80ms);
}
html.js [data-rise].in { opacity: 1; transform: none; }

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  html.js [data-rise] { opacity: 1; transform: none; transition: none; }
  .bar, .btn, .theme-toggle, .link { transition: none; }
}

/* ---------- Footer: a board of filled tiles ---------- */
.board {
  display: grid; grid-template-columns: repeat(12, 1fr);
  gap: 8px; padding: 10px; background: var(--bg);
}
.tile {
  padding: clamp(20px, 2vw, 28px); border-radius: 12px;
  display: flex; flex-direction: column; justify-content: space-between; gap: 16px;
  min-height: 220px;
}
.tile p { font-size: var(--s-body); }
.tile .lead { font-size: var(--s-lead); line-height: 1.2; max-width: 22ch; }
.tile .small { font-size: var(--s-small); }
.tile ul { list-style: none; display: grid; gap: 6px; }
.tile ul a { text-decoration: none; }
.tile ul a:hover { text-decoration: underline; text-underline-offset: .25em; }
.t-statement { grid-column: 1 / 5; }
.t-nav { grid-column: 5 / 8; }
.t-numbers { grid-column: 8 / 10; }
.t-repo { grid-column: 10 / 13; }
.t-name {
  grid-column: 1 / 9; min-height: 320px;
  align-items: center; justify-content: center;
}
.t-name .display { font-size: clamp(3rem, 9vw, 8.25rem); line-height: .9; }
.t-go {
  grid-column: 9 / 13; min-height: 320px; text-decoration: none;
  transition: transform .3s var(--ease-out);
}
.t-go:hover { transform: translateY(-4px); }
.t-go:active { transform: scale(.98); }
.t-go svg { align-self: flex-end; width: 64px; height: 64px; transition: transform .3s var(--ease-out); }
.t-go:hover svg { transform: translate(6px, -6px); }
.numbers { display: grid; gap: 2px; font-size: var(--s-body); }
.numbers b { font-family: var(--display); font-size: var(--s-lead); letter-spacing: -0.02em; }
@media (max-width: 860px) {
  .board { grid-template-columns: 1fr 1fr; gap: 6px; padding: 6px; }
  .t-name { grid-column: 1 / -1; order: -2; min-height: 160px; }
  .t-go { grid-column: 1 / -1; order: -1; min-height: 160px; }
  .t-nav, .t-repo, .t-numbers, .t-statement { grid-column: auto; min-height: 0; }
  .t-go svg { width: 44px; height: 44px; }
}
@media (max-width: 420px) {
  .t-nav, .t-repo, .t-numbers, .t-statement { grid-column: 1 / -1; }
}