/* Shared stylesheet for all concept pages (concepts/<id>/). Same design
   language as the courses; concept pages are shorter and have no topnav.

   Design system: a working textbook. Print-first serif typography, warm
   paper in light mode, warm charcoal in dark (prefers-color-scheme), and
   the vintage-textbook diagram palette — ink, ink-blue, vermilion,
   crimson, green. Mono is reserved for data: readouts, values, counts.
   Canvas widgets read these variables at draw time (see THEME in app.js). */

:root {
  color-scheme: light dark;

  --bg: #f7f3ea;
  --bg-card: #efe9da;
  --border: #d8cfba;
  --text: #211d14;
  --text-dim: #6e6553;
  --accent: #31597f;   /* ink blue — links, primary trace */
  --accent2: #b04e1b;  /* vermilion — labels, secondary trace */
  --hot: #a82433;      /* crimson — warnings, aliases, errors */
  --ok: #3d6b4f;       /* green — mastery, success */
  --ink-rgb: 33, 29, 20;      /* rgb of --text, for translucent washes */
  --paper-rgb: 247, 243, 234; /* rgb of --bg */
  --accent-rgb: 49, 89, 127;
  --hot-rgb: 168, 36, 51;
  --ok-rgb: 61, 107, 79;
  --accent2-rgb: 176, 78, 27;
  --serif: "Iowan Old Style", "Palatino Linotype", Palatino, "Book Antiqua", Georgia, serif;
  --mono: ui-monospace, "SF Mono", Menlo, Consolas, monospace;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #161410;
    --bg-card: #1e1b15;
    --border: #383225;
    --text: #e9e3d3;
    --text-dim: #9c917c;
    --accent: #8fb8e0;
    --accent2: #dd9355;
    --hot: #df7a88;
    --ok: #82bd97;
    --ink-rgb: 233, 227, 211;
    --paper-rgb: 22, 20, 16;
    --accent-rgb: 143, 184, 224;
    --hot-rgb: 223, 122, 136;
    --ok-rgb: 130, 189, 151;
    --accent2-rgb: 221, 147, 85;
  }
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--serif);
  line-height: 1.62;
  font-size: 17.5px;
}

/* ---- site-wide course switcher ---- */
.sitenav {
  max-width: 880px;
  margin: 0 auto;
  padding: 20px 24px 0;
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 12px;
  flex-wrap: wrap;
  font-size: 14.5px;
}

.sitenav .brand {
  color: var(--text);
  text-decoration: none;
  font-weight: 700;
  font-size: 17px;
  letter-spacing: -0.01em;
}

.sitenav .brand span { color: var(--accent2); }

.sitenav .courses {
  display: flex;
  gap: 18px;
  flex-wrap: wrap;
  justify-content: flex-end;
  font-variant-caps: small-caps;
  letter-spacing: 0.03em;
}

.sitenav .courses a {
  color: var(--text-dim);
  text-decoration: none;
}

.sitenav .courses a:hover {
  color: var(--accent);
  text-decoration: underline;
  text-underline-offset: 4px;
}

.sitenav .courses a.current {
  color: var(--text);
  border-bottom: 2px solid var(--accent2);
  padding-bottom: 1px;
}

/* ---- concept header ---- */
header {
  max-width: 880px;
  margin: 0 auto;
  padding: 52px 24px 8px;
}

.concept-tag {
  display: inline-block;
  font-variant-caps: small-caps;
  font-size: 15px;
  letter-spacing: 0.09em;
  color: var(--accent2);
  margin-bottom: 6px;
}

header h1 {
  font-size: clamp(32px, 5vw, 42px);
  font-weight: 600;
  margin: 0 0 14px;
  letter-spacing: -0.01em;
  line-height: 1.15;
  color: var(--text);
}

.intro {
  font-size: 18px;
  color: var(--text);
  margin: 0;
}

.prereq {
  font-size: 14.5px;
  color: var(--text-dim);
  margin: 14px 0 0;
}

.prereq a { color: var(--ok); }

main {
  max-width: 880px;
  margin: 0 auto;
  padding: 0 24px;
}

section { padding: 38px 0 6px; }

section h2 {
  font-size: 25px;
  font-weight: 600;
  letter-spacing: -0.005em;
  margin: 0 0 14px;
}

/* ---- math ---- */
/* Displayed equations sit free on the page, in ink — print convention,
   not a glowing card. */
.math {
  position: relative; /* contain KaTeX's absolutely-positioned MathML copy */
  font-size: 19px;
  text-align: center;
  color: var(--text);
  padding: 10px 18px;
  margin: 26px auto;
  max-width: 720px;
  overflow-x: auto;
}

.math .katex { font-size: 1.22em; }

.tex .katex { font-size: 0.94em; }

.eq-note {
  font-size: 14.5px;
  line-height: 1.6;
  color: var(--text-dim);
  max-width: 700px;
  margin: -14px auto 22px;
  padding: 0 6px 0 16px;
  border-left: 2px solid var(--border);
}

.eq-note strong { color: var(--text); }

/* ---- widgets: instrument panels set into the page like figures ---- */
.widget {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 4px;
  padding: 22px;
  margin: 26px 0 8px;
}

.control-row {
  display: flex;
  align-items: center;
  gap: 14px;
  flex-wrap: wrap;
  margin-bottom: 14px;
}

.control-row label {
  font-size: 14.5px;
  color: var(--text-dim);
  white-space: nowrap;
}

.control-row.sym {
  display: grid;
  grid-template-columns: 88px 1fr 1fr;
  gap: 12px 16px;
  align-items: center;
}

.control-row.sym.single { grid-template-columns: 88px 1fr; }

.ctl {
  display: flex;
  align-items: center;
  gap: 10px;
  min-width: 0;
}

.ctl input[type="range"] {
  flex: 1;
  min-width: 0;
}

.ctl .val {
  flex: none;
  width: 64px;
  text-align: right;
  font-size: 13px;
}

@media (max-width: 600px) {
  .control-row.sym { grid-template-columns: 64px 1fr; }
  .control-row.sym .ctl:nth-of-type(2) { grid-column: 2; }
}

input[type="range"] {
  flex: 1;
  min-width: 110px;
  accent-color: var(--accent);
}

.mono { font-family: var(--mono); }

.dim { color: var(--text-dim); font-size: 13px; }

.btn {
  font-family: var(--mono);
  font-size: 12.5px;
  color: var(--text);
  background: transparent;
  border: 1px solid var(--border);
  border-radius: 3px;
  padding: 6px 13px;
  cursor: pointer;
  transition: border-color 0.15s, color 0.15s;
}

.btn:hover { border-color: var(--accent); color: var(--accent); }

.readout-row {
  display: flex;
  gap: 28px;
  flex-wrap: wrap;
  margin: 14px 0;
}

.readout { text-align: left; }

.readout .big {
  display: block;
  font-size: 28px;
  font-weight: 600;
  color: var(--accent);
  line-height: 1.1;
}

.readout.accent .big { color: var(--accent2); }

.readout small {
  color: var(--text-dim);
  font-size: 12.5px;
}

.plot {
  display: block;
  width: 100%;
  height: 220px;
  margin-top: 8px;
}

.plot.tall { height: 320px; }

.plot.interactive { cursor: grab; touch-action: none; }

.caption {
  font-size: 14.5px;
  font-style: italic;
  color: var(--text-dim);
  margin: 14px 2px 0;
}

.caption .tex .katex { font-style: normal; }

/* ---- mini-quiz (check-in component) ---- */
/* Exercise blocks: a quiet left rule, not a card. */
.checkin {
  border-left: 3px solid var(--ok);
  padding: 4px 0 4px 18px;
  margin: 22px 0 8px;
}

.ck-head {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  gap: 12px;
}

.ck-tag {
  font-variant-caps: small-caps;
  font-size: 14px;
  letter-spacing: 0.08em;
  color: var(--ok);
}

.ck-status {
  font-family: var(--mono);
  font-size: 11.5px;
  color: var(--accent);
}

.ck-q {
  margin: 8px 0 12px;
  font-size: 16px;
}

.ck-options {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.ck-opt.right { border-color: var(--ok); color: var(--ok); }
.ck-opt.right:disabled { opacity: 1; }
.ck-opt.wrong { border-color: var(--hot); color: var(--hot); opacity: 0.55; }
.ck-opt:disabled { cursor: default; }
.ck-opt:disabled:hover { border-color: inherit; color: inherit; }

.btn:disabled {
  opacity: 0.5;
  cursor: default;
}

.ck-why {
  font-size: 14px;
  color: var(--text-dim);
  margin: 12px 2px 0;
  border-top: 1px dashed var(--border);
  padding-top: 10px;
}

.mastered-line {
  font-family: var(--mono);
  font-size: 12.5px;
  color: var(--text-dim);
  margin: 10px 0 0;
}

.mastered-line .ok { color: var(--ok); }

/* ---- used-by backlinks ---- */
.usedby {
  list-style: none;
  margin: 8px 0 0;
  padding: 0;
}

.usedby li {
  font-size: 15px;
  padding: 4px 0;
  color: var(--text-dim);
}

.usedby a { color: var(--accent); text-decoration: none; }

.usedby a:hover { text-decoration: underline; text-underline-offset: 3px; }

/* ---- footer ---- */
footer {
  max-width: 880px;
  margin: 44px auto 0;
  padding: 26px 24px 70px;
  border-top: 1px solid var(--border);
}

.coursenav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
  flex-wrap: wrap;
  font-size: 14.5px;
}

.coursenav a {
  color: var(--accent);
  text-decoration: none;
}

.coursenav a:hover { text-decoration: underline; text-underline-offset: 3px; }

@media (max-width: 560px) {
  .readout .big { font-size: 24px; }
}

/* ---- concepts index (concepts/index.html) ---- */
.cindex { padding-top: 8px; }

.cfilters {
  display: flex;
  align-items: center;
  gap: 12px;
  flex-wrap: wrap;
}

#csearch {
  flex: 1;
  min-width: 240px;
  font-family: var(--serif);
  font-size: 15.5px;
  color: var(--text);
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 3px;
  padding: 10px 14px;
  outline: none;
}

#csearch:focus { border-color: var(--accent); }

#csearch::placeholder { color: var(--text-dim); }

.ctags { display: flex; gap: 6px; flex-wrap: wrap; }

.ctag-btn {
  font-variant-caps: small-caps;
  font-family: var(--serif);
  font-size: 14px;
  letter-spacing: 0.04em;
  color: var(--text-dim);
  background: transparent;
  border: 1px solid var(--border);
  border-radius: 3px;
  padding: 5px 12px;
  cursor: pointer;
  transition: border-color 0.15s, color 0.15s;
}

.ctag-btn:hover { color: var(--accent); border-color: var(--accent); }

.ctag-btn.active { color: var(--accent); border-color: var(--accent); }

.ccount {
  font-family: var(--mono);
  font-size: 12.5px;
  color: var(--text-dim);
  margin: 14px 2px 6px;
}

.cgrid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 18px;
  margin-top: 6px;
}

.ccard {
  display: flex;
  flex-direction: column;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 4px;
  padding: 20px 22px;
  color: inherit;
  text-decoration: none;
  transition: border-color 0.15s;
}

a.ccard:hover { border-color: var(--accent); }

a.ccard:hover h3 { text-decoration: underline; text-underline-offset: 3px; }

.ccard h3 {
  margin: 0 0 6px;
  font-size: 19.5px;
  font-weight: 600;
  letter-spacing: -0.005em;
}

.ccard p {
  margin: 0 0 14px;
  font-size: 14.5px;
  line-height: 1.55;
  color: var(--text-dim);
}

.cmeta {
  display: flex;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
  margin-bottom: 12px;
}

.ctag-chip {
  font-variant-caps: small-caps;
  font-size: 13.5px;
  letter-spacing: 0.06em;
  color: var(--accent2);
}

.cmins {
  font-family: var(--mono);
  font-size: 11px;
  color: var(--text-dim);
  margin-left: auto;
}

.cstate {
  margin-top: auto;
  font-family: var(--mono);
  font-size: 12px;
  color: var(--text-dim);
  border-top: 1px dashed var(--border);
  padding-top: 12px;
}

.cstate .ok { color: var(--ok); }

.cstate .go-hint { color: var(--accent); }

.ccard.planned {
  border-style: dashed;
  background: transparent;
  opacity: 0.75;
}

.cempty {
  font-size: 15.5px;
  color: var(--text-dim);
  padding: 28px 4px;
}

/* Display math shrinks on small screens so simple formulas fit without
   horizontal scrolling; only genuinely wide derivations still scroll. */
@media (max-width: 600px) {
  .math { font-size: 15.5px; padding: 10px 10px; }
  .math .katex { font-size: 1.1em; }
  .eq-note { font-size: 13.5px; }
}

.plot.plane { height: 290px; }

.readout .big.ok { color: var(--ok); }

.readout .big.hot { color: var(--hot); }

/* Inline refresher links to other concept pages: footnote-marker style,
   not a pill. */
.ref {
  display: inline-block;
  font-variant-caps: small-caps;
  font-size: 15px;
  letter-spacing: 0.04em;
  color: var(--ok);
  text-decoration: underline dotted;
  text-underline-offset: 4px;
  margin: 0 2px;
  white-space: nowrap;
}

.ref:hover { text-decoration-style: solid; }

/* Mastery dot appended by the "In the web" panel script. */
.mastered-dot { color: var(--ok); font-weight: 600; }
.prereq.dim { color: var(--text-dim); }

/* Live-updating numbers must not shift layout: tabular figures plus a
   reserved width in ch. Concept readouts show longer strings (complex
   values like "−1.50 − 0.60i"), so they reserve more. */
.mono, .ctl .val, .readout .big, .readout small {
  font-variant-numeric: tabular-nums;
}
.readout .big { min-width: 5ch; }
.plot.plane ~ .readout-row .readout .big, .readout .big.mono { min-width: 9ch; }