/* 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;
  --paper-rgb: 247, 243, 234;
  --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;
}

/* ---- prev/next course pager ---- */
.coursenav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
  flex-wrap: wrap;
  margin-top: 34px;
  padding-top: 18px;
  border-top: 1px dashed var(--border);
  font-size: 14.5px;
}

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

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

footer p a { color: var(--accent); }

.hero {
  max-width: 880px;
  margin: 0 auto;
  padding: 56px 24px 32px;
  text-align: center;
}

.hero h1 {
  font-size: clamp(38px, 6vw, 56px);
  font-weight: 600;
  margin: 0;
  letter-spacing: -0.01em;
  color: var(--text);
}

.hero .amp { font-weight: 300; }

.tagline {
  color: var(--text-dim);
  font-variant-caps: small-caps;
  letter-spacing: 0.07em;
  font-size: 16.5px;
  margin: 8px 0 28px;
}

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

#topnav {
  position: sticky;
  top: 0;
  z-index: 10;
  display: flex;
  justify-content: center;
  flex-wrap: wrap;
  gap: 2px 12px;
  padding: 10px 16px;
  background: rgba(var(--paper-rgb), 0.92);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--border);
}

#topnav a {
  color: var(--text-dim);
  text-decoration: none;
  font-family: var(--mono);
  font-size: 12.5px;
  padding: 5px 2px;
}

#topnav a:hover {
  color: var(--accent);
  text-decoration: underline;
  text-underline-offset: 4px;
}

#topnav a.home { color: var(--accent2); }

#topnav a.done::after {
  content: ' ✓';
  color: var(--ok);
}

#topnav .pill {
  font-family: var(--mono);
  font-size: 12.5px;
  color: var(--accent);
  padding: 5px 2px;
}

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

.lesson { padding: 72px 0 16px; }

.lesson h2 {
  font-size: 30px;
  letter-spacing: -0.01em;
  margin: 0 0 18px;
}

.lesson .num {
  display: inline-block;
  font-size: 0.82em;
  color: var(--accent2);
  margin-right: 12px;
}

.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: 0.92em; }

.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); }

.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: 14px;
  color: var(--text-dim);
  white-space: nowrap;
}

input[type="range"] {
  flex: 1;
  min-width: 160px;
  accent-color: var(--accent);
}

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

.chips {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-bottom: 16px;
}

.chip, .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;
}

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

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

.btn:disabled {
  opacity: 0.35;
  cursor: default;
}

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

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

.readout { text-align: left; }

.readout.inline { margin-left: auto; text-align: right; }

.readout .big {
  display: block;
  font-size: 34px;
  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: 280px; }

.plot.anim { height: 150px; }

.plot.interactive { cursor: ns-resize; 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; }

.stream {
  font-size: 15px;
  letter-spacing: 3px;
  word-break: break-all;
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 12px 14px;
  margin-bottom: 6px;
  user-select: none;
}

.stream .h { color: var(--accent); }
.stream .t { color: var(--accent2); }

.meter {
  height: 10px;
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 99px;
  overflow: hidden;
  margin-top: 14px;
}

.meter-fill {
  height: 100%;
  width: 100%;
  background: linear-gradient(90deg, var(--accent), var(--accent2));
  border-radius: 99px;
  transition: width 0.2s ease;
}

#game-grid {
  display: grid;
  grid-template-columns: repeat(16, 1fr);
  gap: 4px;
  margin-bottom: 18px;
}

#game-grid .cell {
  aspect-ratio: 1;
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--mono);
  font-size: 10.5px;
  color: var(--text-dim);
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 6px;
  transition: opacity 0.35s, background 0.35s, color 0.35s;
}

#game-grid .cell.out { opacity: 0.12; }

#game-grid .cell.found {
  background: var(--accent);
  color: #04141a;
  font-weight: 700;
}

.game-row {
  display: flex;
  align-items: center;
  gap: 16px;
  flex-wrap: wrap;
}

.game-q {
  flex: 1;
  min-width: 220px;
  font-size: 17px;
}

.game-buttons { display: flex; gap: 8px; }

textarea {
  width: 100%;
  resize: vertical;
  font-family: var(--mono);
  font-size: 14px;
  color: var(--text);
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 12px 14px;
  outline: none;
}

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

.readout-row.wide { gap: 36px; }

#freq-table {
  font-family: var(--mono);
  font-size: 13px;
  margin-top: 10px;
}

#freq-table .row {
  display: grid;
  grid-template-columns: 34px 1fr 64px minmax(80px, auto);
  align-items: center;
  gap: 12px;
  padding: 3px 0;
}

#freq-table .bar {
  height: 12px;
  background: linear-gradient(90deg, var(--accent), var(--accent2));
  border-radius: 4px;
  min-width: 2px;
}

#freq-table .code { color: var(--accent2); text-align: right; }
#freq-table .p { color: var(--text-dim); text-align: right; }
#freq-table .ch { color: var(--accent); }

footer {
  max-width: 880px;
  margin: 48px auto 0;
  padding: 48px 24px 80px;
  border-top: 1px solid var(--border);
}

footer h2 { font-size: 24px; }

.books {
  font-size: 14px;
  color: var(--text-dim);
}

.legend {
  display: flex;
  flex-wrap: wrap;
  gap: 18px;
  align-items: center;
  margin-bottom: 10px;
  font-family: var(--mono);
  font-size: 12.5px;
  color: var(--text-dim);
}

.legend .sw {
  display: inline-block;
  width: 12px;
  height: 12px;
  border-radius: 3px;
  margin-right: 7px;
  vertical-align: -1px;
}

.plot.venn { height: 150px; }
.plot.loss { height: 190px; }

.pair-row {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-bottom: 6px;
}

.pair-label {
  flex: none;
  width: 70px;
  text-align: right;
  font-family: var(--mono);
  font-size: 11px;
  color: var(--text-dim);
}

.pair-row .stream {
  flex: 1;
  margin-bottom: 0;
  white-space: nowrap;
  overflow: hidden;
}

.stream .u { color: var(--accent); }
.stream .n { color: #4a5165; }

/* ---- check-ins ---- */
.checkin {
  border-left: 3px solid var(--accent2);
  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(--accent2);
}

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

.ck-q {
  margin: 8px 0 12px;
  font-size: 15.5px;
}

.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:hover { border-color: inherit; color: inherit; }

.ck-why {
  font-size: 13.5px;
  color: var(--text-dim);
  margin: 12px 2px 0;
  border-top: 1px dashed var(--border);
  padding-top: 10px;
}

/* ---- final quiz ---- */
.chips-line {
  font-family: var(--mono);
  font-size: 12px;
  color: var(--text-dim);
  margin-bottom: 14px;
}

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

.quiz-q {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 4px;
  padding: 18px 20px;
  margin: 14px 0;
}

.qq-num {
  font-variant-caps: small-caps;
  font-size: 14px;
  letter-spacing: 0.08em;
  color: var(--accent2);
}

.qq-text {
  margin: 6px 0 12px;
  font-size: 16px;
}

.qq-options {
  display: grid;
  gap: 8px;
}

.qq-opt {
  text-align: left;
  font-family: inherit;
  font-size: 15px;
  line-height: 1.45;
  color: var(--text);
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 3px;
  padding: 9px 14px;
  cursor: pointer;
  transition: border-color 0.15s, color 0.15s;
}

.qq-opt:hover { border-color: var(--accent); }
.qq-opt.sel { border-color: var(--accent); color: var(--accent); background: rgba(var(--accent-rgb), 0.07); }
.qq-opt.right { border-color: var(--ok); color: var(--ok); }
.qq-opt.wrong { border-color: var(--hot); color: var(--hot); }
.qq-opt:disabled { cursor: default; }
.qq-opt:disabled:hover { border-color: var(--border); }
.qq-opt.right:disabled:hover { border-color: var(--ok); }
.qq-opt.wrong:disabled:hover { border-color: var(--hot); }

.qq-why {
  font-size: 13.5px;
  color: var(--text-dim);
  margin: 12px 2px 0;
  border-top: 1px dashed var(--border);
  padding-top: 10px;
}

.quiz-controls {
  display: flex;
  align-items: center;
  gap: 16px;
  flex-wrap: wrap;
  margin-top: 18px;
}

@media (max-width: 560px) {
  #game-grid { grid-template-columns: repeat(8, 1fr); }
  .readout .big { font-size: 27px; }
  .pair-label { width: 56px; }
}

/* 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: 12px 10px; }
  .math .katex { font-size: 1.06em; }
  .eq-note { font-size: 13.5px; }
}

/* Inline refresher links to concept pages: footnote-marker style. */
.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; }

/* Live-updating numbers must not shift layout: tabular figures (a no-op
   where the font is already monospaced) plus a reserved width sized in ch
   so string-length changes stay inside the box. */
.mono, .ctl .val, .readout .big, .readout small, #topnav .pill, .chips-line {
  font-variant-numeric: tabular-nums;
}
.readout .big { min-width: 5ch; }