:root {
  --paper: #f6f2ea;
  --card: #fffdf8;
  --ink: #1d2330;
  --muted: #5d6472;
  --rule: #d9d2c3;
  --teal: #0f5e57;
  --teal-soft: #dcebe8;
  --sin: #c2410c;
  --cos: #1d4ed8;
  --tan: #15803d;
  --warn: #6b4300;
  --warn-bg: #f7ebcf;
  --serif: "Charter", "Iowan Old Style", "Palatino Linotype", Georgia, serif;
  --sans: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", sans-serif;
}

* { box-sizing: border-box; }

html { -webkit-text-size-adjust: 100%; }

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font: 16px/1.6 var(--sans);
}

h1, h2, h3 {
  font-family: var(--serif);
  font-weight: 600;
  letter-spacing: -0.01em;
  line-height: 1.2;
  margin: 0 0 .5em;
}
h1 { font-size: clamp(2rem, 4.5vw, 2.8rem); }
h2 { font-size: 1.6rem; margin-top: 2.2em; padding-top: .8em; border-top: 1px solid var(--rule); }
h2:first-of-type { border-top: 0; margin-top: 1.2em; padding-top: 0; }
h3 { font-size: 1.15rem; margin-top: 1.6em; }

p { margin: .6em 0; }
a { color: var(--teal); }
a:focus-visible, button:focus-visible, input:focus-visible, summary:focus-visible {
  outline: 3px solid var(--teal);
  outline-offset: 3px;
  border-radius: 4px;
}

.kicker {
  font: 600 12px/1 var(--sans);
  letter-spacing: .12em;
  text-transform: uppercase;
  color: var(--teal);
  margin: 0 0 14px;
}

.lede { color: var(--muted); font-size: 1.05rem; max-width: 60ch; }

/* ---------- top bar ---------- */
header.top {
  position: sticky; top: 0; z-index: 10;
  background: rgba(246, 242, 234, .92);
  backdrop-filter: blur(6px);
  border-bottom: 1px solid var(--rule);
}
header.top .wrap {
  max-width: 980px; margin: 0 auto; padding: 12px 20px;
  display: flex; flex-wrap: wrap; align-items: center; gap: 10px 22px;
}
.brand { font: 600 1.05rem var(--serif); color: var(--ink); text-decoration: none; margin-right: auto; }
.brand span { color: var(--muted); font: 13px var(--sans); margin-left: 8px; }
nav.chapters { display: flex; flex-wrap: wrap; gap: 4px 4px; }
nav.chapters a {
  font-size: 14px; color: var(--muted); text-decoration: none;
  padding: 6px 10px; border-radius: 999px;
}
nav.chapters a:hover { color: var(--ink); background: #ebe5d8; }
nav.chapters a[aria-current="page"] { color: var(--teal); background: var(--teal-soft); font-weight: 600; }

main { max-width: 980px; margin: 0 auto; padding: 36px 20px 40px; }

footer {
  max-width: 980px; margin: 0 auto; padding: 0 20px 48px;
  color: var(--muted); font-size: 13px;
  border-top: 1px solid var(--rule); padding-top: 18px;
}

/* ---------- hub ---------- */
.hub-grid {
  display: grid; gap: 16px; margin-top: 28px;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
}
.hub-card {
  display: flex; flex-direction: column; gap: 8px;
  background: var(--card); border: 1px solid var(--rule); border-radius: 14px;
  padding: 22px 22px 20px; text-decoration: none; color: var(--ink);
  transition: transform .15s ease, border-color .15s ease, box-shadow .15s ease;
}
.hub-card:hover { transform: translateY(-2px); border-color: var(--teal); box-shadow: 0 10px 24px -18px rgba(29,35,48,.5); }
.hub-card .num { font: 600 13px var(--sans); color: var(--teal); letter-spacing: .08em; }
.hub-card h2 { font-size: 1.35rem; margin: 0; border: 0; padding: 0; }
.hub-card p { margin: 0; color: var(--muted); font-size: .95rem; }
.hub-card .peek { margin-top: auto; font: 13px var(--sans); color: var(--teal); padding-top: 8px; }
.series-note { margin-top: 36px; color: var(--muted); font-size: 14px; max-width: 64ch; }

/* ---------- formulas ---------- */
.formula {
  background: var(--card); border: 1px solid var(--rule); border-radius: 12px;
  padding: 14px 20px; margin: 12px 0;
  font: 1.2rem/1.5 var(--serif);
  overflow-x: auto;
}
.formula .lbl {
  display: block; font: 600 12px/1.2 var(--sans); letter-spacing: .08em;
  text-transform: uppercase; color: var(--muted); margin-bottom: 6px;
}
.formula .cond { display: block; font: 14px/1.4 var(--sans); color: var(--muted); margin-top: 6px; }
.formula.key { border-color: var(--teal); background: #fbfffd; }

.grid-2 { display: grid; gap: 14px; grid-template-columns: repeat(auto-fit, minmax(280px, 1fr)); }

.note {
  background: var(--warn-bg); color: var(--warn);
  border-radius: 12px; padding: 12px 16px; margin: 16px 0; font-size: .95rem;
}
.note strong { color: #4a2e00; }

.example {
  border: 1px dashed var(--rule); border-radius: 12px; padding: 12px 16px; margin: 14px 0;
  background: #fbf9f3;
}
.example > .lbl { font: 600 12px var(--sans); letter-spacing: .08em; text-transform: uppercase; color: var(--muted); }
.example .calc { font: 1.05rem/1.7 var(--serif); }

details.ans {
  border: 1px solid var(--rule); border-radius: 10px; background: var(--card);
  padding: 10px 14px; margin: 8px 0;
}
details.ans summary { cursor: pointer; font-weight: 600; color: var(--teal); }
details.ans[open] summary { margin-bottom: 8px; }
details.ans .calc { font: 1.05rem/1.7 var(--serif); }

/* ---------- tables ---------- */
.table-wrap { overflow-x: auto; margin: 14px 0; border: 1px solid var(--rule); border-radius: 12px; background: var(--card); }
table { border-collapse: collapse; width: 100%; min-width: 520px; font-variant-numeric: tabular-nums; }
th, td { padding: 9px 12px; text-align: left; border-bottom: 1px solid var(--rule); vertical-align: top; }
tr:last-child td { border-bottom: 0; }
th {
  font: 600 12px/1.2 var(--sans); letter-spacing: .06em; text-transform: uppercase;
  color: var(--muted); background: #f2ede2;
}
td.m { font: 1.08rem var(--serif); white-space: nowrap; }
td.ang { font: 600 15px var(--sans); white-space: nowrap; }
td small { color: var(--muted); }
.s { color: var(--sin); font-weight: 600; }
.c { color: var(--cos); font-weight: 600; }
.t { color: var(--tan); font-weight: 600; }
tr.hl td { background: #f1f7f5; }

/* ---------- quadrant strip ---------- */
.quads { display: grid; gap: 12px; grid-template-columns: repeat(auto-fit, minmax(190px, 1fr)); margin: 14px 0; }
.quad {
  background: var(--card); border: 1px solid var(--rule); border-radius: 12px; padding: 14px 16px;
}
.quad h3 { margin: 0 0 6px; font-size: 1rem; }
.quad .signs { font: 15px/1.9 var(--sans); }
.quad .signs b { display: inline-block; min-width: 3.2em; }
.pos { color: var(--tan); }
.neg { color: #b42318; }

/* ---------- unit circle ---------- */
.circle-wrap {
  display: grid; gap: 22px; align-items: start;
  grid-template-columns: minmax(0, 1fr) minmax(0, 1fr);
}
@media (max-width: 760px) { .circle-wrap { grid-template-columns: 1fr; } }
.figure {
  background: var(--card); border: 1px solid var(--rule); border-radius: 14px; padding: 12px;
}
.figure svg { display: block; width: 100%; height: auto; }
.readout {
  background: var(--card); border: 1px solid var(--rule); border-radius: 14px; padding: 18px 20px;
}
.readout .row { display: grid; grid-template-columns: 4.5em 1fr; gap: 6px 10px; align-items: baseline; padding: 6px 0; border-bottom: 1px solid #ece6d8; }
.readout .row:last-child { border-bottom: 0; }
.readout .k { font: 600 13px var(--sans); color: var(--muted); }
.readout .v { font: 1.25rem var(--serif); overflow-wrap: anywhere; }
.readout .v small { font: 14px var(--sans); color: var(--muted); }
.controls { display: flex; flex-direction: column; gap: 12px; margin-bottom: 14px; }
.controls label { font: 600 13px var(--sans); color: var(--muted); display: flex; justify-content: space-between; }
.controls input[type=range] { width: 100%; accent-color: var(--teal); }
.presets { display: flex; flex-wrap: wrap; gap: 6px; }
.presets button {
  font: 600 13px var(--sans); color: var(--ink); background: #f2ede2;
  border: 1px solid var(--rule); border-radius: 999px; padding: 6px 11px; cursor: pointer;
  min-height: 36px;
}
.presets button:hover { border-color: var(--teal); color: var(--teal); }
.presets button[aria-pressed="true"] { background: var(--teal); color: #fff; border-color: var(--teal); }
.legend { display: flex; flex-wrap: wrap; gap: 6px 16px; font-size: 14px; margin-top: 10px; color: var(--muted); }
.legend span::before { content: ""; display: inline-block; width: 14px; height: 4px; border-radius: 2px; margin-right: 6px; vertical-align: middle; background: currentColor; }
.legend .ls::before { color: var(--sin); }
.legend .lc::before { color: var(--cos); }
.legend .lt::before { color: var(--tan); }

/* ---------- prev / next ---------- */
.pager { display: flex; justify-content: space-between; gap: 12px; margin-top: 40px; flex-wrap: wrap; }
.pager a {
  flex: 1 1 240px; background: var(--card); border: 1px solid var(--rule); border-radius: 12px;
  padding: 14px 16px; text-decoration: none; color: var(--ink);
}
.pager a:hover { border-color: var(--teal); }
.pager small { display: block; color: var(--muted); font-size: 12px; letter-spacing: .06em; text-transform: uppercase; }
.pager .next { text-align: right; }

/* ---------- print ---------- */
@media print {
  header.top, .pager, .controls, details.ans summary { display: none; }
  details.ans { border: 0; padding: 0; }
  details.ans > *:not(summary) { display: block !important; }
  body { background: #fff; }
  .formula, .example, .quad, .readout, .figure, .table-wrap, .note { break-inside: avoid; }
}

@media (prefers-reduced-motion: reduce) {
  * { transition: none !important; }
}