/* ==========================================================================
   Engineerspedia — stylesheet
   Category colours are NOT hardcoded here. Each category supplies its own
   colour from data/site.json, injected as the custom property --cat.
   That means adding a discipline needs zero CSS changes.
   ========================================================================== */

/* --- Design tokens ------------------------------------------------------ */
:root {
  --bg:        #fbfaf8;
  --surface:   #ffffff;
  --surface-2: #f4f3ef;
  --ink:       #15181d;
  --ink-2:     #3d4653;
  --muted:     #626c7a;
  --line:      #e5e3dd;
  --line-2:    #d5d2ca;
  --accent:    #1f4fd8;
  --accent-ink:#ffffff;
  --blueprint: #12315f;
  --code-bg:   #f4f3ef;
  --shadow:    0 1px 2px rgba(16, 24, 40, .05), 0 8px 24px -12px rgba(16, 24, 40, .16);
  --shadow-lg: 0 2px 4px rgba(16, 24, 40, .05), 0 18px 40px -18px rgba(16, 24, 40, .26);
  --radius:    14px;
  --radius-sm: 9px;
  --maxw:      1120px;
  --readw:     50rem;
  --font: ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto,
          "Helvetica Neue", Arial, "Noto Sans", sans-serif;
  --mono: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas,
          "Liberation Mono", monospace;
  color-scheme: light;
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg:        #0e1116;
    --surface:   #151a21;
    --surface-2: #1b222b;
    --ink:       #e7eaf0;
    --ink-2:     #c2c9d4;
    --muted:     #98a2b1;
    --line:      #242c36;
    --line-2:    #333d49;
    --accent:    #7ea2ff;
    --accent-ink:#0e1116;
    --blueprint: #0a1c36;
    --code-bg:   #11161d;
    --shadow:    0 1px 2px rgba(0, 0, 0, .4), 0 8px 24px -12px rgba(0, 0, 0, .6);
    --shadow-lg: 0 2px 4px rgba(0, 0, 0, .4), 0 18px 40px -18px rgba(0, 0, 0, .7);
    color-scheme: dark;
  }
}

/* Explicit dark choice wins in both directions. */
:root[data-theme="dark"] {
  --bg:        #0e1116;
  --surface:   #151a21;
  --surface-2: #1b222b;
  --ink:       #e7eaf0;
  --ink-2:     #c2c9d4;
  --muted:     #98a2b1;
  --line:      #242c36;
  --line-2:    #333d49;
  --accent:    #7ea2ff;
  --accent-ink:#0e1116;
  --blueprint: #0a1c36;
  --code-bg:   #11161d;
  --shadow:    0 1px 2px rgba(0, 0, 0, .4), 0 8px 24px -12px rgba(0, 0, 0, .6);
  --shadow-lg: 0 2px 4px rgba(0, 0, 0, .4), 0 18px 40px -18px rgba(0, 0, 0, .7);
  color-scheme: dark;
}

/* --- Base --------------------------------------------------------------- */
*, *::before, *::after { box-sizing: border-box; }

html { -webkit-text-size-adjust: 100%; scroll-behavior: smooth; }
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { animation-duration: .01ms !important; transition-duration: .01ms !important; }
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--font);
  font-size: 1rem;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

img, svg { max-width: 100%; height: auto; }

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

h1, h2, h3, h4, h5 {
  margin: 0 0 .5em;
  line-height: 1.22;
  letter-spacing: -.018em;
  font-weight: 700;
  text-wrap: balance;
}
h1 { font-size: clamp(1.9rem, 1.2rem + 2.6vw, 3rem); }
h2 { font-size: clamp(1.35rem, 1.1rem + 1vw, 1.75rem); }
h3 { font-size: 1.15rem; }

p { margin: 0 0 1.1em; }

:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 3px;
  border-radius: 4px;
}

.container {
  width: 100%;
  max-width: var(--maxw);
  margin-inline: auto;
  padding-inline: 20px;
}

.skip-link {
  position: absolute;
  left: -9999px;
  top: 0;
  background: var(--accent);
  color: var(--accent-ink);
  padding: 10px 16px;
  z-index: 100;
  border-radius: 0 0 8px 0;
}
.skip-link:focus { left: 0; }

/* --- Header / nav ------------------------------------------------------- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background: color-mix(in srgb, var(--bg) 88%, transparent);
  backdrop-filter: saturate(160%) blur(10px);
  border-bottom: 1px solid var(--line);
}

.nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  max-width: var(--maxw);
  margin-inline: auto;
  padding: 12px 20px;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  color: var(--ink);
  font-weight: 700;
  font-size: 1.05rem;
  letter-spacing: -.02em;
}
.brand:hover { text-decoration: none; }

.brand .mark {
  display: grid;
  place-items: center;
  width: 34px;
  height: 34px;
  flex: 0 0 34px;
  border-radius: 9px;
  background: var(--blueprint);
  color: #fff;
  font-size: .82rem;
  font-weight: 700;
  letter-spacing: .01em;
}

.brand .sub {
  display: block;
  font-size: .72rem;
  font-weight: 500;
  color: var(--muted);
  letter-spacing: 0;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 4px;
  list-style: none;
  margin: 0 0 0 auto;   /* push the links (and everything after) to the right */
  padding: 0;
}
.nav-links a {
  display: block;
  padding: 8px 12px;
  border-radius: 8px;
  color: var(--ink-2);
  font-size: .92rem;
  font-weight: 500;
}
.nav-links a:hover { background: var(--surface-2); text-decoration: none; color: var(--ink); }
.nav-links a.active { color: var(--ink); font-weight: 650; }

.nav-cta {
  background: var(--ink);
  color: var(--bg) !important;
  margin-left: 6px;
}
.nav-cta:hover { background: var(--ink-2); color: var(--bg) !important; }

.nav-toggle {
  display: none;
  background: none;
  border: 1px solid var(--line-2);
  border-radius: 8px;
  color: var(--ink);
  font-size: 1.1rem;
  line-height: 1;
  padding: 8px 11px;
  cursor: pointer;
}

.theme-toggle {
  display: inline-grid;
  place-items: center;
  background: none;
  border: 1px solid var(--line-2);
  border-radius: 8px;
  color: var(--ink-2);
  cursor: pointer;
  line-height: 1;
  padding: 8px 10px;
}
.theme-toggle:hover { background: var(--surface-2); color: var(--ink); }

@media (max-width: 860px) {
  .brand { order: 1; }
  .theme-toggle { order: 2; }
  .nav-toggle { display: block; order: 3; }
  .nav-links {
    order: 4;
    margin-left: 0;
    flex-basis: 100%;
    flex-direction: column;
    align-items: stretch;
    gap: 2px;
    padding-top: 10px;
  }
  .nav-links[hidden] { display: none; }
  .nav-links a { padding: 11px 12px; }
  .nav-cta { margin-left: 0; text-align: center; }
  .nav { flex-wrap: wrap; }
}

/* --- Blueprint backdrop ------------------------------------------------- */
.blueprint-bg {
  position: relative;
  background-color: var(--blueprint);
  background-image:
    linear-gradient(rgba(255, 255, 255, .08) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255, 255, 255, .08) 1px, transparent 1px),
    linear-gradient(rgba(255, 255, 255, .04) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255, 255, 255, .04) 1px, transparent 1px);
  background-size: 96px 96px, 96px 96px, 24px 24px, 24px 24px;
  color: #fff;
}
.blueprint-bg h1,
.blueprint-bg h2 { color: #fff; }
.blueprint-bg a:not(.btn):not(.card-tag) { color: #cfe0ff; }
.blueprint-bg p { color: rgba(255, 255, 255, .82); }
.blueprint-bg .btn-primary { color: var(--blueprint); }
.blueprint-bg .btn-ghost { color: #fff; }

/* --- Hero --------------------------------------------------------------- */
.hero {
  padding-block: clamp(52px, 8vw, 92px);
  text-align: center;
}
.hero .eyebrow {
  display: inline-block;
  padding: 5px 12px;
  border: 1px solid rgba(255, 255, 255, .28);
  border-radius: 999px;
  font-size: .78rem;
  letter-spacing: .06em;
  text-transform: uppercase;
  color: rgba(255, 255, 255, .82);
  margin-bottom: 18px;
}
.hero p.lede {
  max-width: 40rem;
  margin: 0 auto 26px;
  font-size: clamp(1rem, .95rem + .4vw, 1.18rem);
}

.btn-row { display: flex; flex-wrap: wrap; gap: 12px; justify-content: center; }

.btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 11px 20px;
  border-radius: 10px;
  border: 1px solid transparent;
  font-size: .95rem;
  font-weight: 600;
  cursor: pointer;
  font-family: inherit;
}
.btn:hover { text-decoration: none; }
.btn-primary { background: #fff; color: var(--blueprint); }
.btn-primary:hover { background: #e9eefb; }
.btn-ghost { border-color: rgba(255, 255, 255, .4); color: #fff; }
.btn-ghost:hover { background: rgba(255, 255, 255, .1); }

.hero-stats {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 12px 36px;
  margin-top: 34px;
  padding-top: 26px;
  border-top: 1px solid rgba(255, 255, 255, .16);
}
.hero-stats div { text-align: center; }
.hero-stats strong { display: block; font-size: 1.45rem; }
.hero-stats span { font-size: .82rem; color: rgba(255, 255, 255, .68); }

/* --- Sections ----------------------------------------------------------- */
section { padding-block: clamp(40px, 5vw, 68px); }
section.tight { padding-block: clamp(28px, 3vw, 40px); }

.section-head {
  display: flex;
  align-items: end;
  justify-content: space-between;
  gap: 16px;
  margin-bottom: 24px;
  flex-wrap: wrap;
}
.section-head h2 { margin: 0; }
.section-head p { margin: 6px 0 0; color: var(--muted); font-size: .95rem; }
.section-head .read-link { font-size: .92rem; font-weight: 600; white-space: nowrap; }

/* --- Cards -------------------------------------------------------------- */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 22px;
}

.card {
  display: flex;
  flex-direction: column;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  overflow: hidden;
  box-shadow: var(--shadow);
  transition: transform .18s ease, box-shadow .18s ease, border-color .18s ease;
}
.card:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-lg);
  border-color: var(--line-2);
}

.card-media {
  display: grid;
  place-items: center;
  height: 118px;
  font-size: 2.4rem;
  background:
    linear-gradient(135deg,
      color-mix(in srgb, var(--cat, var(--accent)) 88%, #000 4%),
      color-mix(in srgb, var(--cat, var(--accent)) 52%, #fff 30%));
  background-color: var(--cat, var(--accent));
}

.card-body { padding: 18px 18px 16px; display: flex; flex-direction: column; flex: 1; }
.card-body h3 { font-size: 1.08rem; margin: 10px 0 8px; }
.card-body h3 a { color: var(--ink); }
.card-body h3 a:hover { color: var(--accent); }
.card-body p { color: var(--muted); font-size: .92rem; margin: 0 0 14px; }

.card-meta {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
  margin-top: auto;
  padding-top: 12px;
  border-top: 1px solid var(--line);
  font-size: .84rem;
  color: var(--muted);
}
.read-link { font-weight: 600; color: var(--accent); }

/* Category pill — colour comes entirely from --cat. */
.card-tag {
  display: inline-block;
  align-self: flex-start;
  padding: 4px 10px;
  border-radius: 999px;
  font-size: .74rem;
  font-weight: 650;
  letter-spacing: .02em;
  background: color-mix(in srgb, var(--cat, var(--accent)) 15%, transparent);
  color: color-mix(in srgb, var(--cat, var(--accent)) 82%, var(--ink) 18%);
  border: 1px solid color-mix(in srgb, var(--cat, var(--accent)) 28%, transparent);
}
:root[data-theme="dark"] .card-tag {
  color: color-mix(in srgb, var(--cat, var(--accent)) 62%, #fff 38%);
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) .card-tag {
    color: color-mix(in srgb, var(--cat, var(--accent)) 62%, #fff 38%);
  }
}
.blueprint-bg .card-tag {
  background: rgba(255, 255, 255, .16);
  color: #fff;
  border-color: rgba(255, 255, 255, .28);
}

/* --- Category tiles ----------------------------------------------------- */
.cat-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  gap: 18px;
}

.cat-tile {
  display: block;
  position: relative;
  padding: 20px 20px 18px;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  border-left: 4px solid var(--cat, var(--accent));
  box-shadow: var(--shadow);
  color: var(--ink);
  transition: transform .18s ease, box-shadow .18s ease;
}
.cat-tile:hover { transform: translateY(-3px); box-shadow: var(--shadow-lg); text-decoration: none; }
.cat-tile .cat-emoji { font-size: 1.7rem; display: block; margin-bottom: 10px; }
.cat-tile h3 { margin: 0 0 6px; font-size: 1.05rem; }
.cat-tile p { margin: 0 0 12px; font-size: .9rem; color: var(--muted); }
.cat-tile .count { font-size: .82rem; font-weight: 600; color: var(--cat, var(--accent)); }

/* Raw category hues can go too dark against a dark ground — lift them. */
:root[data-theme="dark"] .cat-tile .count,
:root[data-theme="dark"] .cat-section-head .cat-emoji {
  color: color-mix(in srgb, var(--cat, var(--accent)) 58%, #fff 42%);
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) .cat-tile .count {
    color: color-mix(in srgb, var(--cat, var(--accent)) 58%, #fff 42%);
  }
}

/* --- Category sections (categories.html) -------------------------------- */
.cat-section { scroll-margin-top: 84px; padding-block: 0; margin-bottom: 44px; }
.cat-section-head {
  display: flex;
  align-items: center;
  gap: 14px;
  padding-bottom: 14px;
  margin-bottom: 22px;
  border-bottom: 2px solid var(--cat, var(--accent));
}
.cat-section-head .cat-emoji { font-size: 1.9rem; }
.cat-section-head h2 { margin: 0; }
.cat-section-head p { margin: 2px 0 0; color: var(--muted); font-size: .92rem; }
.cat-section-head .count {
  margin-left: auto;
  font-size: .84rem;
  color: var(--muted);
  white-space: nowrap;
}

/* --- Filters / search --------------------------------------------------- */
.toolbar {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 26px;
}

.chip-row { display: flex; flex-wrap: wrap; gap: 8px; }

.chip {
  padding: 7px 14px;
  border-radius: 999px;
  border: 1px solid var(--line-2);
  background: var(--surface);
  color: var(--ink-2);
  font-size: .87rem;
  font-family: inherit;
  font-weight: 550;
  cursor: pointer;
  transition: background .15s ease, color .15s ease, border-color .15s ease;
}
.chip:hover { border-color: var(--cat, var(--accent)); color: var(--ink); }
.chip[aria-pressed="true"] {
  background: var(--cat, var(--ink));
  border-color: var(--cat, var(--ink));
  color: #fff;
}

.search-box {
  flex: 1 1 220px;
  max-width: 320px;
  padding: 9px 14px;
  border: 1px solid var(--line-2);
  border-radius: 10px;
  background: var(--surface);
  color: var(--ink);
  font-family: inherit;
  font-size: .92rem;
}
.search-box::placeholder { color: var(--muted); }

.result-count { color: var(--muted); font-size: .88rem; margin-bottom: 18px; }

.empty-state {
  text-align: center;
  padding: 60px 20px;
  color: var(--muted);
  border: 1px dashed var(--line-2);
  border-radius: var(--radius);
}

/* --- Article ------------------------------------------------------------ */
.article-hero { padding-block: clamp(38px, 5vw, 60px); }
.crumbs { font-size: .85rem; color: rgba(255, 255, 255, .7); margin-bottom: 14px; }
.crumbs a { color: rgba(255, 255, 255, .92); }

.article-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 8px 20px;
  margin-top: 16px;
  font-size: .88rem;
  color: rgba(255, 255, 255, .78);
}

.article-body {
  max-width: var(--readw);
  margin: 0 auto;
  padding: clamp(34px, 5vw, 56px) 20px;
  font-size: 1.07rem;
  line-height: 1.75;
  color: var(--ink-2);
}
.article-body > h2 {
  margin-top: 2em;
  padding-top: .2em;
  color: var(--ink);
}
.article-body > h3 { margin-top: 1.7em; color: var(--ink); }
.article-body strong { color: var(--ink); font-weight: 650; }
.article-body ul, .article-body ol { margin: 0 0 1.2em; padding-left: 1.35em; }
.article-body li { margin-bottom: .6em; }
.article-body li::marker { color: var(--muted); }

.article-body code {
  font-family: var(--mono);
  font-size: .89em;
  background: var(--code-bg);
  border: 1px solid var(--line);
  border-radius: 5px;
  padding: .12em .38em;
}
.article-body pre {
  background: var(--code-bg);
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  padding: 16px 18px;
  overflow-x: auto;
  margin: 0 0 1.4em;
  line-height: 1.55;
}
.article-body pre code {
  background: none;
  border: 0;
  padding: 0;
  font-size: .88rem;
}

.callout {
  background: color-mix(in srgb, var(--cat, var(--accent)) 8%, var(--surface));
  border: 1px solid color-mix(in srgb, var(--cat, var(--accent)) 26%, transparent);
  border-left: 4px solid var(--cat, var(--accent));
  border-radius: var(--radius-sm);
  padding: 16px 18px;
  margin: 0 0 1.5em;
  font-size: .98rem;
}
.callout p:last-child { margin-bottom: 0; }
.callout strong { color: var(--ink); }

.article-body blockquote {
  margin: 1.8em 0;
  padding: 4px 0 4px 22px;
  border-left: 3px solid var(--cat, var(--accent));
  font-size: 1.13rem;
  line-height: 1.6;
  font-style: italic;
  color: var(--ink);
}

.article-divider { border: 0; border-top: 1px solid var(--line); margin: 2.4em 0 1.6em; }

.tag-row { display: flex; flex-wrap: wrap; gap: 8px; }
.tag-pill {
  padding: 5px 11px;
  border-radius: 999px;
  background: var(--surface-2);
  border: 1px solid var(--line);
  font-size: .8rem;
  color: var(--muted);
}

.related-grid { background: var(--surface-2); border-top: 1px solid var(--line); }

/* --- Prose pages (about / contact) -------------------------------------- */
.prose {
  max-width: var(--readw);
  margin: 0 auto;
  padding: clamp(34px, 5vw, 56px) 20px;
  font-size: 1.05rem;
  line-height: 1.72;
  color: var(--ink-2);
}
.prose h2 { margin-top: 1.9em; color: var(--ink); }
.prose ul { padding-left: 1.35em; }
.prose li { margin-bottom: .5em; }

.field { margin-bottom: 16px; }
.field label { display: block; font-size: .9rem; font-weight: 600; margin-bottom: 6px; color: var(--ink); }
.field input, .field select, .field textarea {
  width: 100%;
  padding: 10px 13px;
  border: 1px solid var(--line-2);
  border-radius: 10px;
  background: var(--surface);
  color: var(--ink);
  font-family: inherit;
  font-size: .95rem;
}
.field textarea { min-height: 140px; resize: vertical; }
.btn-solid {
  background: var(--accent);
  color: var(--accent-ink);
  border: 0;
  padding: 11px 22px;
  border-radius: 10px;
  font-family: inherit;
  font-size: .95rem;
  font-weight: 600;
  cursor: pointer;
}
.btn-solid:hover { filter: brightness(1.08); }

/* --- Newsletter strip --------------------------------------------------- */
.subscribe {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: clamp(24px, 4vw, 38px);
  text-align: center;
  box-shadow: var(--shadow);
}
.subscribe h2 { margin-bottom: 8px; }
.subscribe p { color: var(--muted); max-width: 34rem; margin-inline: auto; }
.subscribe form {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  justify-content: center;
  margin-top: 20px;
}
.subscribe input {
  flex: 1 1 260px;
  max-width: 340px;
  padding: 11px 15px;
  border: 1px solid var(--line-2);
  border-radius: 10px;
  background: var(--bg);
  color: var(--ink);
  font-family: inherit;
  font-size: .95rem;
}

/* --- Footer ------------------------------------------------------------- */
.site-footer {
  background: var(--surface);
  border-top: 1px solid var(--line);
  padding-block: 44px 22px;
  margin-top: 20px;
}
.footer-grid {
  display: grid;
  grid-template-columns: 1.6fr repeat(4, 1fr);
  gap: 32px;
}
.footer-grid h5 {
  margin: 0 0 12px;
  font-size: .78rem;
  letter-spacing: .08em;
  text-transform: uppercase;
  color: var(--muted);
}
.footer-grid ul { list-style: none; margin: 0; padding: 0; }
.footer-grid li { margin-bottom: 8px; }
.footer-grid a { color: var(--ink-2); font-size: .92rem; }
.footer-grid a:hover { color: var(--accent); }
.footer-grid p { color: var(--muted); }

.footer-bottom {
  display: flex;
  flex-wrap: wrap;
  gap: 8px 20px;
  justify-content: space-between;
  margin-top: 34px;
  padding-top: 18px;
  border-top: 1px solid var(--line);
  font-size: .85rem;
  color: var(--muted);
}

@media (max-width: 760px) {
  .footer-grid { grid-template-columns: 1fr 1fr; gap: 26px; }
}
@media (max-width: 440px) {
  .footer-grid { grid-template-columns: 1fr; }
  .card-grid { grid-template-columns: 1fr; }
}

/* --- Utilities ---------------------------------------------------------- */
.visually-hidden {
  position: absolute;
  width: 1px; height: 1px;
  padding: 0; margin: -1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
  white-space: nowrap;
  border: 0;
}
.loading { color: var(--muted); padding: 40px 0; text-align: center; }