/* ===== Waves revision notes — screen + A4 print ===== */
:root {
  --ink: #1b2130;
  --muted: #5d6677;
  --line: #d9dde5;
  --paper: #ffffff;
  --bg: #eef0f4;
  --accent: #2456c9;
  --accent-soft: #eaf0fd;
  --star: #c77700;
  --star-soft: #fff5e3;
  --ok: #17803d;
  --radius: 10px;
  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", Inter, Roboto, "Helvetica Neue", Arial, sans-serif;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font: 15px/1.55 var(--font);
  -webkit-print-color-adjust: exact;
  print-color-adjust: exact;
}

/* ---------- toolbar ---------- */
.toolbar {
  position: sticky; top: 0; z-index: 10;
  display: flex; flex-wrap: wrap; gap: 8px; align-items: center;
  padding: 10px 16px;
  background: rgba(255,255,255,.92);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--line);
}
.toolbar .title { font-weight: 700; margin-right: auto; }
.toolbar nav { display: flex; gap: 4px; flex-wrap: wrap; }
.toolbar nav a {
  color: var(--muted); text-decoration: none; font-size: 13px;
  padding: 4px 10px; border-radius: 999px;
}
.toolbar nav a:hover { background: var(--accent-soft); color: var(--accent); }
button, .btn {
  font: inherit; font-size: 13px; cursor: pointer;
  border: 1px solid var(--line); background: #fff; color: var(--ink);
  padding: 6px 12px; border-radius: 8px;
}
button:hover { border-color: var(--accent); color: var(--accent); }
button.primary { background: var(--accent); color: #fff; border-color: var(--accent); }
button.primary:hover { filter: brightness(1.08); color: #fff; }
label.check { font-size: 13px; color: var(--muted); display: flex; gap: 6px; align-items: center; }

/* ---------- page ---------- */
main { max-width: 880px; margin: 24px auto 80px; padding: 0 16px; }
.chapter {
  background: var(--paper);
  border-radius: 14px;
  box-shadow: 0 1px 3px rgba(0,0,0,.06), 0 8px 24px rgba(0,0,0,.04);
  padding: 36px 44px 28px;
  margin-bottom: 28px;
}
.chapter-head { border-bottom: 3px solid var(--accent); padding-bottom: 12px; margin-bottom: 20px; }
.chapter-head .kicker { font-size: 12px; letter-spacing: .12em; text-transform: uppercase; color: var(--accent); font-weight: 700; }
.chapter-head h1 { margin: 2px 0 6px; font-size: 28px; line-height: 1.2; }
.chapter-head .outcomes { margin: 0; padding-left: 18px; color: var(--muted); font-size: 14px; }

h2 {
  font-size: 18px; margin: 28px 0 10px;
  display: flex; align-items: center; gap: 8px;
}
h2::before {
  content: ""; width: 6px; height: 18px; border-radius: 3px; background: var(--accent);
}
h3 { font-size: 15px; margin: 18px 0 6px; }
p { margin: 6px 0; }
ul, ol { margin: 6px 0; padding-left: 20px; }
li { margin: 2px 0; }
strong { font-weight: 650; }
.muted { color: var(--muted); }
.small { font-size: 13px; }
hr.soft { border: 0; border-top: 1px dashed var(--line); margin: 18px 0; }

/* ---------- blocks ---------- */
.grid2 { display: grid; grid-template-columns: 1fr 1fr; gap: 14px 22px; }
.grid3 { display: grid; grid-template-columns: repeat(3, 1fr); gap: 12px; }

.card {
  border: 1px solid var(--line); border-radius: var(--radius);
  padding: 12px 14px; background: #fff;
  break-inside: avoid;
}
.card h3 { margin-top: 0; }

.key {
  position: relative;
  border: 1.5px solid var(--star); background: var(--star-soft);
  border-radius: var(--radius); padding: 10px 14px 10px 40px; margin: 10px 0;
  break-inside: avoid;
}
.key::before {
  content: "★"; position: absolute; left: 13px; top: 8px;
  color: var(--star); font-size: 18px;
}
.key .tag {
  display: block; font-size: 11px; font-weight: 700; letter-spacing: .1em;
  text-transform: uppercase; color: var(--star);
}

.formula-row { display: flex; flex-wrap: wrap; gap: 10px; margin: 10px 0; }
.formula {
  font-family: "Cambria Math", "STIX Two Math", Georgia, serif;
  font-size: 20px; padding: 8px 18px;
  border: 2px solid var(--accent); border-radius: 8px;
  background: var(--accent-soft); color: var(--ink);
  break-inside: avoid;
}
.formula small { font-family: var(--font); font-size: 12px; color: var(--muted); margin-left: 8px; }
.var { font-family: "Cambria Math", Georgia, serif; font-style: italic; }

table.data { border-collapse: collapse; width: 100%; font-size: 14px; margin: 8px 0; }
table.data th, table.data td { border: 1px solid var(--line); padding: 6px 10px; text-align: left; vertical-align: top; }
table.data th { background: #f4f6f9; font-weight: 650; }
table.data td.num { text-align: right; font-variant-numeric: tabular-nums; }

.compare { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; }
.compare .card.accent { border-color: var(--accent); background: var(--accent-soft); }

/* ---------- figures ---------- */
figure { margin: 12px 0; break-inside: avoid; }
figure svg { width: 100%; height: auto; display: block; }
figcaption { font-size: 12.5px; color: var(--muted); text-align: center; margin-top: 4px; }

svg text { font-family: var(--font); font-size: 13px; fill: var(--ink); }
svg text.sm { font-size: 11px; fill: var(--muted); }
svg text.lbl { font-weight: 650; }
svg text.acc { fill: var(--accent); }
svg text.star { fill: var(--star); }
svg text.big { font-size: 16px; font-weight: 700; }
svg .ax { stroke: var(--ink); stroke-width: 1.4; fill: none; }
svg .grid { stroke: #e4e7ee; stroke-width: 1; }
svg .guide { stroke: var(--muted); stroke-width: 1; stroke-dasharray: 4 4; fill: none; }
svg .wave { stroke: var(--accent); stroke-width: 2.6; fill: none; stroke-linecap: round; }
svg .wave.ink { stroke: var(--ink); }
svg .wave.mut { stroke: #9aa3b2; stroke-dasharray: 6 5; }
svg .wave.thin { stroke-width: 1.8; }
svg .arrow { stroke: var(--ink); stroke-width: 1.6; fill: none; }
svg .arrow.a { stroke: var(--accent); }
svg .arrow.s { stroke: var(--star); stroke-width: 2.2; }
svg .solid { fill: #cfd5df; stroke: #8b94a3; stroke-width: 1; }
svg .pt { fill: var(--ink); }
svg .pt.a { fill: var(--star); }
svg a:hover rect { filter: brightness(.93); }

/* ---------- worked examples ---------- */
.example {
  border-left: 4px solid var(--ink); background: #f7f8fa;
  border-radius: 0 var(--radius) var(--radius) 0;
  padding: 10px 14px; margin: 14px 0; break-inside: avoid;
}
.example .ex-title { font-weight: 700; font-size: 13px; letter-spacing: .06em; text-transform: uppercase; color: var(--muted); }
details.ans { margin-top: 8px; }
details.ans summary {
  cursor: pointer; font-size: 13px; font-weight: 650; color: var(--accent);
  list-style: none; display: inline-block; padding: 2px 10px; border: 1px solid var(--accent); border-radius: 999px;
}
details.ans summary::-webkit-details-marker { display: none; }
details.ans[open] summary { background: var(--accent); color: #fff; }
details.ans .body {
  margin-top: 8px; padding: 8px 12px; background: #fff; border: 1px dashed var(--accent); border-radius: 8px;
}
.working { font-family: "Cambria Math", Georgia, serif; font-size: 16px; line-height: 1.7; }
.working .final { font-weight: 700; color: var(--ok); }

/* ---------- interactive labs (screen only) ---------- */
.lab {
  border: 1.5px dashed var(--accent); border-radius: var(--radius);
  padding: 12px 14px; margin: 14px 0; background: #fbfcff;
}
.lab .lab-title { font-size: 12px; font-weight: 700; letter-spacing: .1em; text-transform: uppercase; color: var(--accent); margin-bottom: 6px; }
.lab .controls { display: flex; flex-wrap: wrap; gap: 10px 20px; align-items: center; font-size: 13.5px; }
.lab input[type=range] { width: 150px; accent-color: var(--accent); vertical-align: middle; }
.lab input[type=number] { width: 96px; font: inherit; padding: 4px 6px; border: 1px solid var(--line); border-radius: 6px; }
.lab output, .readout { font-variant-numeric: tabular-nums; font-weight: 650; }
.readout { display: inline-block; background: var(--accent-soft); color: var(--accent); padding: 3px 10px; border-radius: 6px; }
.seg { display: inline-flex; border: 1px solid var(--line); border-radius: 8px; overflow: hidden; }
.seg button { border: 0; border-radius: 0; }
.seg button.on { background: var(--accent); color: #fff; }

.spectrum-info { min-height: 44px; font-size: 14px; }

/* ---------- print ---------- */
@page { size: A4; margin: 13mm 13mm 14mm; }

@media print {
  body { background: #fff; font-size: 10.4pt; line-height: 1.42; }
  .toolbar, .no-print, .lab { display: none !important; }
  main { max-width: none; margin: 0; padding: 0; }
  .chapter { box-shadow: none; border-radius: 0; padding: 0; margin: 0; break-before: page; }
  .chapter:first-of-type { break-before: auto; }
  h2 { break-after: avoid; margin-top: 16px; }
  h3 { break-after: avoid; }
  figure, .card, .key, .example, table { break-inside: avoid; }
  .chapter-head h1 { font-size: 22pt; }
  details.ans summary { display: none; }
  details.ans .body { border-style: solid; }
  body.print-no-answers details.ans { display: none; }
  a { color: inherit; text-decoration: none; }
}

@media (max-width: 680px) {
  .chapter { padding: 22px 16px; }
  .grid2, .compare { grid-template-columns: 1fr; }
  .grid3 { grid-template-columns: 1fr 1fr; }
  .toolbar nav { display: none; }
  .chapter-head h1 { font-size: 23px; }
}

@media (prefers-reduced-motion: reduce) { html { scroll-behavior: auto; } }