/* ==========================================================================
   Components — Nav, hero, cards, article, callouts, footer
   ========================================================================== */

/* --- Grain overlays (CSS pseudo-elements) ------------------------------- */

body::after {
  content: '';
  position: fixed;
  top: 0; left: 0; width: 100%; height: 100%;
  background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 512 512' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='noise'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.75' numOctaves='5' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23noise)' opacity='0.5'/%3E%3C/svg%3E");
  opacity: 0.18;
  pointer-events: none;
  z-index: var(--z-grain-top);
  mix-blend-mode: luminosity;
}

body::before {
  content: '';
  position: fixed;
  top: 0; left: 0; width: 100%; height: 100%;
  background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 256 256' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='noise2'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='1.2' numOctaves='3' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23noise2)' opacity='0.6'/%3E%3C/svg%3E");
  opacity: 0.1;
  pointer-events: none;
  z-index: var(--z-grain);
  mix-blend-mode: luminosity;
}

/* --- Canvas elements ---------------------------------------------------- */

.hero-canvas,
.card canvas,
.article-bg-canvas {
  position: absolute;
  top: 0; left: 0;
  width: 100%; height: 100%;
  filter: blur(0.3px);
}

#siteBgCanvas {
  position: fixed;
  top: 0; left: 0;
  width: 100%; height: 100%;
  z-index: var(--z-bg);
  pointer-events: none;
}

/* --- Navigation --------------------------------------------------------- */

nav {
  position: fixed;
  top: 0; left: 0; right: 0;
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: var(--space-m) var(--gutter);
  z-index: var(--z-nav);
}

.nav-bg {
  position: absolute;
  top: 0; left: 0;
  width: 100%; height: 100%;
  z-index: -1;
  opacity: 0;
  transition: opacity 0.4s ease;
}

nav.scrolled .nav-bg { opacity: 1; }

.logo {
  color: var(--white);
  text-decoration: none;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: var(--space-l);
  list-style: none;
  margin: 0;
  padding: 0;
}

.nav-links a {
  color: var(--off-white);
  text-decoration: none;
  opacity: 0.7;
  transition: opacity 0.3s;
}

.nav-links a:hover { opacity: 1; }

/* Hamburger button — hidden on desktop */
.nav-toggle {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  padding: 4px;
  z-index: 2;
}

.nav-toggle span {
  display: block;
  width: 24px;
  height: 2px;
  background: var(--white);
  margin: 6px 0;
  transition: transform 0.3s var(--ease-out), opacity 0.2s;
}

/* Animate to X when open */
nav.nav-open .nav-toggle span:nth-child(1) {
  transform: translateY(8px) rotate(45deg);
}

nav.nav-open .nav-toggle span:nth-child(2) {
  opacity: 0;
}

nav.nav-open .nav-toggle span:nth-child(3) {
  transform: translateY(-8px) rotate(-45deg);
}

@media (max-width: 768px) {
  .nav-toggle { display: block; }

  .nav-links {
    position: fixed;
    top: 0; right: 0;
    width: 100%; height: 100vh;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    gap: 40px;
    background: var(--blue);
    opacity: 0;
    pointer-events: none;
    transition: opacity 0.3s ease;
    z-index: 1;
  }

  .nav-links a {
    font-size: 18px;
    opacity: 0.9;
  }

  nav.nav-open .nav-links {
    opacity: 1;
    pointer-events: auto;
  }
}

/* --- Hero --------------------------------------------------------------- */

.hero {
  position: relative;
  height: 100vh;
  min-height: 700px;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  padding: var(--gutter);
  background: transparent;
  overflow: hidden;
}

.hero-content {
  position: relative;
  z-index: 10;
  padding-bottom: var(--gutter);
}

.hero-title {
  margin-bottom: var(--space-m);
}

.hero-subtitle {
  opacity: 0.7;
  max-width: 400px;
  line-height: 1.6;
  margin-left: 4px;
}

.hero-date {
  position: absolute;
  top: 100px;
  right: var(--gutter);
  opacity: 0.5;
  z-index: 10;
}

/* --- Featured card ------------------------------------------------------ */

.featured-card {
  background: var(--card-bg);
  padding: clamp(32px, 4vw, 60px);
}

.featured-card + .featured-card {
  margin-top: 20px;
}

.featured-card .section-label {
  color: var(--text-heading);
  opacity: 0.35;
}

.section-label {
  opacity: 0.4;
  margin-bottom: var(--space-xl);
}

/* --- Part headers ------------------------------------------------------- */

.part-header {
  margin-bottom: 40px;
}

.part-label {
  display: block;
  font-size: 11px;
  letter-spacing: 2px;
  text-transform: uppercase;
  color: var(--text-heading);
  opacity: 0.35;
  margin-bottom: var(--space-xs);
}

.part-title {
  font-family: 'Cormorant Garamond', serif;
  font-weight: 600;
  font-size: 36px;
  color: var(--text-heading);
  letter-spacing: 0;
}

/* --- Supporting modules — muted treatment ------------------------------- */

.featured-card--supporting {
  background: var(--callout-bg);
}

.featured-card--supporting .part-label {
  opacity: 0.3;
}

.featured-card--supporting .part-title {
  opacity: 0.75;
}

/* --- Topic cards (blue squares) ----------------------------------------- */

.card {
  position: relative;
  aspect-ratio: 1;
  background: var(--blue);
  overflow: hidden;
  cursor: pointer;
  transition: transform 0.4s var(--ease-out);
}

a.card {
  color: inherit;
  text-decoration: none;
}

.card:hover { transform: scale(0.97); }

.card-content {
  position: absolute;
  bottom: 0; left: 0; right: 0;
  padding: var(--space-m);
  z-index: 2;
}

.card-tag { opacity: 0.5; margin-bottom: var(--space-xs); }

.card-number {
  position: absolute;
  top: 20px; right: 20px;
  opacity: 0.4;
}

/* --- Expandable derivation cards ---------------------------------------- */

.article-derivation {
  background: var(--callout-bg);
  margin: 40px 0;
  max-width: 640px;
}

.derivation-result {
  padding: 28px 32px 0;
}

.derivation-result p {
  margin-bottom: 0;
}

.derivation-toggle {
  display: block;
  background: none;
  border: none;
  font-family: 'DM Sans', sans-serif;
  font-size: 12px;
  letter-spacing: 1px;
  text-transform: uppercase;
  color: var(--blue);
  cursor: pointer;
  padding: 16px 32px 20px;
  opacity: 0.7;
  transition: opacity 0.2s;
}

.derivation-toggle:hover { opacity: 1; }

.derivation-body {
  display: none;
  padding: 0 32px 28px;
  border-top: 1px solid #d0cec8;
}

.derivation-open .derivation-body {
  display: block;
}

.derivation-body p,
.derivation-body .article-eq {
  font-size: 15px;
}

/* --- Problem cards ------------------------------------------------------- */

.article-problem {
  background: var(--callout-bg);
  margin: 40px 0;
  max-width: 640px;
  border-left: 3px solid var(--blue);
}

.article-problems {
  margin-top: 56px;
  padding-top: 32px;
  border-top: 1px solid #d8d6d0;
}

.article-problem p,
.article-problem .article-eq {
  color: var(--text-body);
}

.problem-question {
  padding: 28px 32px 0;
}

.problem-question p {
  margin-bottom: 0;
}

/* --- Display equations --------------------------------------------------- */

.article-eq {
  margin: 32px 0;
  text-align: center;
  font-size: 18px;
  color: var(--text-heading);
  overflow-x: auto;
}

/* --- Lists -------------------------------------------------------------- */

.article-list {
  font-family: 'Lora', serif;
  font-size: 16px;
  line-height: 1.75;
  color: var(--text-body);
  max-width: 640px;
  margin-bottom: var(--space-s);
  padding-left: 24px;
}

.article-list li {
  margin-bottom: 6px;
}

/* --- Figures ------------------------------------------------------------ */

.article-figure {
  max-width: 640px;
  margin: 40px 0;
}

.article-figure img {
  width: 100%;
  height: auto;
  display: block;
}

.article-figure figcaption {
  font-family: 'DM Sans', sans-serif;
  font-size: 12px;
  letter-spacing: 0.3px;
  color: var(--text-muted);
  margin-top: 12px;
  line-height: 1.5;
}

/* --- Interactive widgets ------------------------------------------------ */

.article-widget {
  max-width: 640px;
  margin: 40px 0;
  background: var(--callout-bg);
  position: relative;
  min-height: 300px;
}

.widget-canvas {
  display: block;
  width: 100%;
}

.widget-controls {
  padding: 20px 24px;
  display: flex;
  flex-wrap: wrap;
  gap: 16px;
  align-items: center;
}

.widget-label {
  font-family: 'DM Sans', sans-serif;
  font-size: 12px;
  letter-spacing: 0.5px;
  text-transform: uppercase;
  color: var(--text-body);
}

.widget-slider {
  -webkit-appearance: none;
  appearance: none;
  height: 3px;
  background: #c8c6d0;
  outline: none;
  flex: 1;
  min-width: 100px;
}

.widget-slider::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 14px;
  height: 14px;
  background: var(--blue);
  cursor: pointer;
}

.widget-value {
  font-family: 'Lora', serif;
  font-size: 14px;
  color: var(--text-heading);
  min-width: 48px;
  text-align: right;
}

/* --- Browse list -------------------------------------------------------- */

.topic-row {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  padding: 28px 0;
  border-bottom: 1px solid rgba(240, 240, 248, 0.08);
  cursor: pointer;
  transition: all 0.3s;
}

.topic-row:hover {
  padding-left: 12px;
  border-bottom-color: rgba(240, 240, 248, 0.2);
}

.topic-row:first-child {
  border-top: 1px solid rgba(240, 240, 248, 0.08);
}

.topic-row:hover .topic-name { color: var(--blue-light); }

.topic-name { transition: color 0.3s; }
.topic-count { opacity: 0.3; }

/* --- Article ------------------------------------------------------------ */

.article-card {
  background: var(--card-bg);
  padding: clamp(40px, 5vw, 80px);
}

.article-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: var(--space-l);
}

.article-title { margin-bottom: 20px; }
.article-intro { margin-bottom: var(--space-xl); }

.article-body h3 {
  margin-bottom: var(--space-s);
  margin-top: var(--space-xl);
}

.article-body h3:first-child { margin-top: 0; }
.article-body p { margin-bottom: var(--space-s); }

.article-breadcrumb {
  display: inline-block;
  opacity: 0.4;
  color: var(--white);
  text-decoration: none;
  margin-bottom: var(--space-m);
  transition: opacity 0.3s;
}

a.article-breadcrumb:hover {
  opacity: 0.7;
}

/* --- Callout ------------------------------------------------------------ */

.article-callout {
  background: var(--callout-bg);
  padding: 28px 32px;
  margin: 40px 0;
}

.callout-label { margin-bottom: 12px; }
.article-callout p { margin-bottom: 0; }

/* --- References --------------------------------------------------------- */

.article-refs {
  margin-top: 56px;
  padding-top: var(--space-l);
  border-top: 1px solid #d8d6d0;
}

.refs-label { margin-bottom: var(--space-s); }

.ref-link {
  display: inline-block;
  font-size: 13px;
  color: var(--blue);
  text-decoration: none;
  padding: 6px 14px;
  border: 1px solid #d0cec8;
  margin-right: var(--space-xs);
  margin-bottom: var(--space-xs);
  transition: all 0.2s;
}

.ref-link:hover {
  background: var(--blue);
  color: var(--white);
  border-color: var(--blue);
}

/* --- Article prev/next navigation --------------------------------------- */

.article-nav {
  display: flex;
  justify-content: space-between;
  max-width: 900px;
  border-top: 1px solid #d8d6d0;
  background: var(--card-bg);
}

.article-nav a {
  display: flex;
  flex-direction: column;
  text-decoration: none;
  padding: 32px clamp(32px, 4vw, 48px);
  flex: 1;
  transition: background 0.3s;
}

.article-nav a:hover {
  background: var(--callout-bg);
}

.article-nav-next { text-align: right; }
.article-nav-prev { text-align: left; }

/* Hide empty placeholder slots */
.article-nav a:empty,
.article-nav-placeholder {
  display: none;
}

/* When only next exists, push it right */
.article-nav a:only-child.article-nav-next {
  margin-left: auto;
}

.article-nav-label {
  font-size: 11px;
  letter-spacing: 1.5px;
  text-transform: uppercase;
  color: var(--text-muted);
  margin-bottom: 8px;
}

.article-nav-title {
  font-family: 'Cormorant Garamond', serif;
  font-weight: 600;
  font-size: 22px;
  color: var(--text-heading);
  line-height: 1.25;
  transition: color 0.3s;
}

.article-nav a:hover .article-nav-title {
  color: var(--blue);
}

@media (max-width: 768px) {
  .article-nav { flex-direction: column; }
  .article-nav-next { text-align: left; }
}

/* --- Section landing page (module overview) ------------------------------ */

.section-card {
  margin-bottom: 0;
}

.section-card .article-intro {
  margin-bottom: 0;
}

.section-list {
  margin-top: 20px;
  background: var(--card-bg);
  max-width: 900px;
}

.section-row {
  display: flex;
  align-items: baseline;
  gap: var(--space-m);
  padding: 28px clamp(32px, 4vw, 48px);
  border-top: 1px solid #d8d6d0;
  text-decoration: none;
  transition: all 0.3s;
  cursor: pointer;
}

.section-row:hover {
  background: var(--callout-bg);
  padding-left: clamp(40px, 4.5vw, 56px);
}

.section-row-number {
  font-family: 'Instrument Serif', serif;
  font-size: 18px;
  color: var(--blue);
  opacity: 0.4;
  flex-shrink: 0;
  min-width: 32px;
}

.section-row-body {
  flex: 1;
  min-width: 0;
}

.section-row-title {
  display: block;
  font-family: 'Cormorant Garamond', serif;
  font-weight: 600;
  font-size: 22px;
  color: var(--text-heading);
  letter-spacing: 0;
  line-height: 1.2;
  margin-bottom: 4px;
  transition: color 0.3s;
}

.section-row:hover .section-row-title {
  color: var(--blue);
}

.section-row-desc {
  display: block;
  font-family: 'Lora', serif;
  font-size: 14px;
  line-height: 1.5;
  color: var(--text-body);
  opacity: 0.7;
}

.section-row-time {
  font-size: 12px;
  color: var(--text-muted);
  flex-shrink: 0;
  letter-spacing: 0.5px;
}

.section-row--draft {
  opacity: 0.45;
}

.section-row--draft:hover {
  opacity: 0.65;
}

@media (max-width: 768px) {
  .section-row {
    flex-wrap: wrap;
    gap: var(--space-xs);
    padding: 20px var(--gutter-mobile);
  }
  .section-row-time {
    width: 100%;
    padding-left: 56px;
  }
  .section-row-title { font-size: 18px; }
}

/* --- Footer ------------------------------------------------------------- */

footer {
  padding: var(--gutter);
  display: flex;
  justify-content: space-between;
  align-items: center;
  border-top: 1px solid rgba(240, 240, 248, 0.06);
  font-size: 12px;
  opacity: 0.3;
}

/* --- Entrance animations ------------------------------------------------ */

@keyframes fadeUp {
  from { opacity: 0; transform: translateY(30px); }
  to   { opacity: 1; transform: translateY(0); }
}

.hero-content { animation: fadeUp 1s   var(--ease-out) 0.3s both; }
.hero-date    { animation: fadeUp 0.8s var(--ease-out) 0.6s both; }