/* =====================================================
   Metrology for Engineering Technicians — Web Edition
   Accessible stylesheet (WCAG 2.1 AA / WAVE friendly)
   ===================================================== */

:root {
  --ink: #1b2733;          /* body text — 14.9:1 on white */
  --ink-soft: #3d4c5c;     /* secondary text — 8.6:1 */
  --brand: #0a4a7a;        /* headings — 8.9:1 */
  --brand-mid: #0b5394;    /* links/buttons — 7.4:1 on white */
  --brand-pale: #eaf2f9;
  --accent-warm: #8a3c00;  /* warm accent — 7.5:1 */
  --ok-dark: #1e5e20;
  --warn-bg: #fdf3e7;
  --paper: #ffffff;
  --paper-alt: #f5f8fb;
  --line: #c3d2de;
  --focus: #b35c00;
  --max-w: 52rem;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { animation: none !important; transition: none !important; }
}

body {
  margin: 0;
  font-family: Georgia, 'Times New Roman', serif;
  font-size: 1.075rem;
  line-height: 1.65;
  color: var(--ink);
  background: var(--paper);
}

h1, h2, h3, h4, nav, .btn, .site-header, .site-footer, .toc-card,
.calc, .quiz, figcaption, summary, .badge, .crumbs, table {
  font-family: 'Segoe UI', Verdana, Arial, sans-serif;
}

/* ---------- Skip link ---------- */
.skip-link {
  position: absolute;
  left: -999px;
  top: 0;
  background: var(--brand);
  color: #ffffff;
  padding: 0.7rem 1.2rem;
  z-index: 100;
  font-weight: 600;
  text-decoration: none;
}
.skip-link:focus {
  left: 0.5rem;
  top: 0.5rem;
  outline: 3px solid var(--focus);
  outline-offset: 2px;
}

/* ---------- Header & nav ---------- */
.site-header {
  background: var(--brand);
  color: #ffffff;
  padding: 0.9rem 1rem;
}
.site-header .wrap {
  max-width: var(--max-w);
  margin: 0 auto;
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: 0.35rem 1rem;
}
.site-title {
  font-size: 1.15rem;
  font-weight: 700;
  margin: 0;
}
.site-title a { color: #ffffff; text-decoration: none; }
.site-title a:hover, .site-title a:focus { text-decoration: underline; }
.site-sub { font-size: 0.9rem; color: #d7e5f2; margin: 0; }

.site-nav {
  background: #083a60;
  padding: 0.4rem 1rem;
}
.site-nav ul {
  max-width: var(--max-w);
  margin: 0 auto;
  padding: 0;
  list-style: none;
  display: flex;
  flex-wrap: wrap;
  gap: 0.2rem;
}
.site-nav a {
  display: block;
  color: #ffffff;
  text-decoration: none;
  padding: 0.45rem 0.7rem;
  border-radius: 4px;
  font-size: 0.95rem;
}
.site-nav a:hover { background: #0b5394; text-decoration: underline; }
.site-nav a[aria-current="page"] {
  background: #ffffff;
  color: var(--brand);
  font-weight: 700;
}

/* ---------- Layout ---------- */
main {
  max-width: var(--max-w);
  margin: 0 auto;
  padding: 1.5rem 1rem 3rem;
}

h1 { color: var(--brand); font-size: 1.9rem; line-height: 1.25; margin: 0.5rem 0 1rem; }
h2 { color: var(--brand); font-size: 1.45rem; margin: 2.2rem 0 0.7rem; border-bottom: 2px solid var(--line); padding-bottom: 0.25rem; }
h3 { color: var(--ink); font-size: 1.15rem; margin: 1.5rem 0 0.5rem; }
h4 { color: var(--ink-soft); font-size: 1.02rem; margin: 1.2rem 0 0.4rem; }

p, ul, ol { margin: 0.6rem 0 1rem; }
li { margin: 0.25rem 0; }

a { color: var(--brand-mid); }
a:hover { color: var(--brand); }

:focus-visible {
  outline: 3px solid var(--focus);
  outline-offset: 2px;
  border-radius: 2px;
}

strong.term { color: var(--brand); }

.lede { font-size: 1.12rem; color: var(--ink-soft); }

.crumbs { font-size: 0.9rem; margin: 0 0 1rem; color: var(--ink-soft); }

/* ---------- Boxes ---------- */
.example, .practice, .keyidea, .note-box {
  border-radius: 8px;
  padding: 1rem 1.2rem;
  margin: 1.2rem 0;
  border: 1px solid var(--line);
}
.example { background: var(--brand-pale); border-left: 6px solid var(--brand-mid); }
.practice { background: #f3f7ee; border-left: 6px solid #3c6e1f; }
.keyidea { background: var(--warn-bg); border-left: 6px solid var(--accent-warm); }
.note-box { background: var(--paper-alt); }

.example h3, .example h4, .practice h3, .practice h4 { margin-top: 0.2rem; }

.formula {
  font-family: 'Cambria Math', Cambria, Georgia, serif;
  background: var(--paper-alt);
  border: 1px solid var(--line);
  border-radius: 6px;
  padding: 0.6rem 1rem;
  margin: 0.8rem 0;
  overflow-x: auto;
  font-size: 1.1rem;
}

/* ---------- Answer reveal ---------- */
details.answer {
  margin: 0.8rem 0 0.2rem;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: #ffffff;
}
details.answer summary {
  cursor: pointer;
  padding: 0.6rem 0.9rem;
  font-weight: 600;
  color: var(--brand-mid);
}
details.answer summary:hover { background: var(--brand-pale); }
details.answer[open] summary { border-bottom: 1px solid var(--line); }
details.answer .answer-body { padding: 0.7rem 1rem; }

/* ---------- Figures ---------- */
figure {
  margin: 1.6rem 0;
  padding: 1rem;
  background: var(--paper-alt);
  border: 1px solid var(--line);
  border-radius: 8px;
  text-align: center;
}
figure svg { max-width: 100%; height: auto; }
figcaption {
  margin-top: 0.7rem;
  font-size: 0.92rem;
  color: var(--ink-soft);
  text-align: left;
}
figcaption strong { color: var(--brand); }

/* ---------- Tables ---------- */
table {
  border-collapse: collapse;
  width: 100%;
  margin: 1rem 0;
  font-size: 0.97rem;
}
caption {
  text-align: left;
  font-weight: 700;
  color: var(--brand);
  padding-bottom: 0.4rem;
}
th, td {
  border: 1px solid var(--line);
  padding: 0.45rem 0.7rem;
  text-align: left;
}
th { background: var(--brand-pale); color: var(--ink); }
tbody tr:nth-child(even) { background: var(--paper-alt); }
.table-scroll { overflow-x: auto; }

/* ---------- Interactive widgets ---------- */
.calc, .quiz {
  border: 2px solid var(--brand-mid);
  border-radius: 10px;
  padding: 1.1rem 1.3rem;
  margin: 1.8rem 0;
  background: #ffffff;
}
.calc h3, .quiz h3 { margin-top: 0; color: var(--brand); }
.calc .hint, .quiz .hint { font-size: 0.9rem; color: var(--ink-soft); }

.field {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.5rem;
  margin: 0.6rem 0;
}
.field label { font-weight: 600; min-width: 13rem; }
input[type="number"], input[type="text"], select {
  font: inherit;
  padding: 0.4rem 0.55rem;
  border: 1px solid #5a6b7a;
  border-radius: 5px;
  min-width: 9rem;
  background: #ffffff;
  color: var(--ink);
}

.btn {
  font-size: 1rem;
  font-weight: 600;
  color: #ffffff;
  background: var(--brand-mid);
  border: none;
  border-radius: 6px;
  padding: 0.55rem 1.1rem;
  cursor: pointer;
  margin: 0.5rem 0.4rem 0.2rem 0;
}
.btn:hover { background: var(--brand); }
.btn-secondary { background: #4d5f70; }
.btn-secondary:hover { background: #37454f; }

.result {
  margin-top: 0.8rem;
  padding: 0.7rem 1rem;
  border-radius: 6px;
  background: var(--brand-pale);
  border: 1px solid var(--line);
  min-height: 1.4rem;
}
.result:empty { display: none; }
.result.good { background: #edf5ea; border-color: #3c6e1f; }
.result.bad { background: var(--warn-bg); border-color: var(--accent-warm); }

/* quiz options */
.quiz fieldset {
  border: 1px solid var(--line);
  border-radius: 8px;
  margin: 1rem 0;
  padding: 0.8rem 1rem;
}
.quiz legend { font-weight: 700; padding: 0 0.4rem; }
.quiz .opt {
  display: flex;
  gap: 0.5rem;
  align-items: baseline;
  margin: 0.35rem 0;
}
.quiz .opt label { font-weight: 400; }

/* ---------- TOC cards on index ---------- */
.toc-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(15rem, 1fr));
  gap: 0.9rem;
  padding: 0;
  margin: 1.2rem 0;
  list-style: none;
}
.toc-card {
  border: 1px solid var(--line);
  border-left: 6px solid var(--brand-mid);
  border-radius: 8px;
  background: var(--paper-alt);
}
.toc-card a {
  display: block;
  padding: 0.9rem 1rem;
  text-decoration: none;
  color: var(--brand);
  font-weight: 700;
  height: 100%;
}
.toc-card a:hover { background: var(--brand-pale); text-decoration: underline; }
.toc-card .num {
  display: block;
  font-size: 0.8rem;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--ink-soft);
  font-weight: 600;
}

.badge {
  display: inline-block;
  background: var(--brand-pale);
  color: var(--brand);
  font-size: 0.8rem;
  font-weight: 700;
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 0.1rem 0.7rem;
  margin-right: 0.4rem;
}

/* ---------- Prev/next pager ---------- */
.pager {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin-top: 2.5rem;
  border-top: 2px solid var(--line);
  padding-top: 1.2rem;
  flex-wrap: wrap;
}
.pager a {
  font-family: 'Segoe UI', Verdana, sans-serif;
  font-weight: 600;
  text-decoration: none;
  padding: 0.6rem 1rem;
  border: 1px solid var(--brand-mid);
  border-radius: 6px;
  color: var(--brand-mid);
}
.pager a:hover { background: var(--brand-pale); text-decoration: underline; }

/* ---------- Footer ---------- */
.site-footer {
  background: #083a60;
  color: #ffffff;
  padding: 1.4rem 1rem;
  margin-top: 2rem;
  font-size: 0.92rem;
}
.site-footer .wrap { max-width: var(--max-w); margin: 0 auto; }
.site-footer a { color: #cfe3f5; }

/* ---------- Print ---------- */
@media print {
  .site-nav, .skip-link, .pager, .btn { display: none; }
  body { font-size: 11pt; }
}