/* =========================================
   MathPi — Apple-Inspired Design System
   ========================================= */

/* 1. Design Tokens */
:root {
  /* Apple's exact palette */
  --white:    #ffffff;
  --bg:       #f5f5f7;       /* Apple's signature light gray */
  --bg-2:     #fafafa;
  --border:   #d2d2d7;       /* Apple's border color */
  --border-2: #e8e8ed;

  --t1: #1d1d1f;             /* Apple primary text */
  --t2: #6e6e73;             /* Apple secondary text */
  --t3: #a1a1a6;             /* Apple tertiary / placeholder */

  /* Brand */
  --navy:      #1b2d4f;
  --navy-2:    #2e4a77;
  --gold:      #bf9030;
  --gold-pale: #fdf6e3;

  /* Radii */
  --r-sm: 8px;
  --r-md: 14px;
  --r-lg: 20px;
  --r-xl: 28px;

  /* Shadows */
  --s1: 0 1px 3px rgba(0,0,0,.06), 0 1px 2px rgba(0,0,0,.04);
  --s2: 0 4px 16px rgba(0,0,0,.08), 0 2px 4px rgba(0,0,0,.04);
  --s3: 0 8px 28px rgba(0,0,0,.10), 0 4px 8px rgba(0,0,0,.05);
  --s4: 0 16px 48px rgba(0,0,0,.12), 0 8px 14px rgba(0,0,0,.06);

  /* Nav height — used for sticky offsets */
  --nav-h: 52px;
}

/* 2. Reset */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Helvetica Neue', sans-serif;
  background: var(--white);
  color: var(--t1);
  line-height: 1.6;
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
  overflow-x: hidden;
}

/* =========================================
   3. Navigation — Apple translucent blur
   ========================================= */
#site-header {
  position: sticky;
  top: 0;
  z-index: 200;
  /* Exact Apple nav treatment */
  background: rgba(255, 255, 255, 0.82);
  backdrop-filter: saturate(180%) blur(20px);
  -webkit-backdrop-filter: saturate(180%) blur(20px);
  border-bottom: 1px solid rgba(0, 0, 0, 0.08);
}

.nav-wrap {
  max-width: 1080px;
  margin: 0 auto;
  padding: 0 24px;
  height: var(--nav-h);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
}

.nav-logo {
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--t1);
  text-decoration: none;
  letter-spacing: -0.3px;
  flex-shrink: 0;
}
.nav-logo-pi { color: var(--gold); margin-left: 1px; }

.nav-links {
  display: flex;
  align-items: center;
  gap: 2px;
}
.nav-links a {
  font-size: 0.82rem;
  font-weight: 400;
  color: var(--t2);
  text-decoration: none;
  padding: 5px 11px;
  border-radius: 6px;
  transition: color .13s, background .13s;
  white-space: nowrap;
}
.nav-links a:hover { color: var(--t1); background: rgba(0,0,0,.04); }
.nav-links a.active { color: var(--navy); font-weight: 600; }

/* Hamburger (three lines → animated X) */
.nav-hamburger {
  display: none;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  width: 34px;
  height: 34px;
  gap: 5px;
  border: none;
  background: transparent;
  cursor: pointer;
  border-radius: 6px;
  transition: background .13s;
  flex-shrink: 0;
}
.nav-hamburger:hover { background: rgba(0,0,0,.05); }
.nav-hamburger span {
  display: block;
  width: 18px;
  height: 1.5px;
  background: var(--t1);
  border-radius: 2px;
  transition: transform .22s, opacity .22s;
  transform-origin: center;
}
.nav-hamburger.open span:nth-child(1) { transform: translateY(6.5px) rotate(45deg); }
.nav-hamburger.open span:nth-child(2) { opacity: 0; transform: scaleX(0); }
.nav-hamburger.open span:nth-child(3) { transform: translateY(-6.5px) rotate(-45deg); }

/* Mobile drawer */
.nav-mobile-drawer {
  display: none;
  flex-direction: column;
  background: rgba(255,255,255,.97);
  backdrop-filter: blur(20px);
  border-top: 1px solid var(--border-2);
  padding: 8px 0 14px;
}
.nav-mobile-drawer.open { display: flex; }
.nav-mobile-drawer a {
  padding: 12px 28px;
  font-size: .95rem;
  font-weight: 500;
  color: var(--t1);
  text-decoration: none;
  transition: background .12s;
}
.nav-mobile-drawer a:hover { background: var(--bg); }

/* =========================================
   4. Homepage — Hero (full-width, Apple-scale)
   ========================================= */
.hero {
  text-align: center;
  padding: 110px 24px 80px;
  border-bottom: 1px solid var(--border-2);
  background: var(--white);
}

.hero-eyebrow {
  display: inline-block;
  font-size: 0.75rem;
  font-weight: 600;
  letter-spacing: 2px;
  text-transform: uppercase;
  color: var(--gold);
  margin-bottom: 20px;
}

.hero h1 {
  font-size: clamp(2.8rem, 6.5vw, 5.2rem);
  font-weight: 700;
  letter-spacing: -0.03em;
  line-height: 1.06;
  color: var(--t1);
  max-width: 760px;
  margin: 0 auto 18px;
  /* override global */
  border: none;
  padding: 0;
}
.hero-accent { color: var(--navy); }

.hero-sub {
  font-size: 1.05rem;
  color: var(--t2);
  max-width: 520px;
  margin: 0 auto 36px;
  line-height: 1.6;
  font-weight: 400;
}

.hero-cta {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 12px;
  flex-wrap: wrap;
}

.btn-primary {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: var(--navy);
  color: var(--white);
  text-decoration: none;
  font-size: .9rem;
  font-weight: 600;
  padding: 12px 24px;
  border-radius: 980px;
  transition: background .18s, transform .18s;
  letter-spacing: .1px;
}
.btn-primary:hover { background: var(--navy-2); transform: scale(1.02); }

.btn-ghost {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  color: var(--navy);
  text-decoration: none;
  font-size: .9rem;
  font-weight: 600;
  padding: 12px 24px;
  border-radius: 980px;
  border: 1.5px solid var(--navy);
  letter-spacing: .1px;
  transition: background .18s, color .18s;
}
.btn-ghost:hover { background: var(--navy); color: var(--white); }

/* =========================================
   5. Stats Bar
   ========================================= */
.stats-bar {
  display: flex;
  justify-content: center;
  align-items: stretch;
  background: var(--bg);
  border-bottom: 1px solid var(--border-2);
}
.stat {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 28px 52px;
  border-right: 1px solid var(--border);
}
.stat:last-child { border-right: none; }
.stat-num {
  font-size: 2rem;
  font-weight: 700;
  letter-spacing: -0.04em;
  color: var(--navy);
  line-height: 1;
}
.stat-label {
  font-size: .75rem;
  color: var(--t2);
  margin-top: 5px;
  letter-spacing: .2px;
}

/* =========================================
   6. Home Content Sections
   ========================================= */
.home-section {
  max-width: 1040px;
  margin: 0 auto;
  padding: 80px 24px;
}

.section-eyebrow {
  font-size: .72rem;
  font-weight: 600;
  letter-spacing: 2.2px;
  text-transform: uppercase;
  color: var(--gold);
  margin-bottom: 10px;
}
.section-headline {
  font-size: clamp(1.8rem, 3.5vw, 2.4rem);
  font-weight: 700;
  letter-spacing: -.025em;
  line-height: 1.15;
  color: var(--t1);
  margin-top: 0;
  margin-bottom: 8px;
}
.section-sub {
  font-size: .95rem;
  color: var(--t2);
  margin-bottom: 40px;
  max-width: 480px;
}

/* =========================================
   7. Cards
   ========================================= */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(270px, 1fr));
  gap: 16px;
}

.card {
  background: var(--bg);
  border: 1px solid var(--border-2);
  border-radius: var(--r-lg);
  padding: 34px 28px 28px;
  text-decoration: none;
  color: var(--t1);
  display: flex;
  flex-direction: column;
  position: relative;
  overflow: hidden;
  transition: box-shadow .25s, transform .25s, background .18s;
}
.card::after {
  content: '';
  position: absolute;
  inset: 0;
  border-radius: inherit;
  background: linear-gradient(135deg, rgba(255,255,255,.6) 0%, transparent 60%);
  pointer-events: none;
}
.card:hover {
  background: var(--white);
  box-shadow: var(--s4);
  transform: translateY(-5px) scale(1.005);
}

.card-icon {
  font-size: 2.4rem;
  line-height: 1;
  margin-bottom: 18px;
  display: block;
  transition: transform .3s cubic-bezier(.175,.885,.32,1.275);
}
.card:hover .card-icon { transform: scale(1.12); }

.card-title {
  font-size: 1rem;
  font-weight: 700;
  color: var(--t1);
  letter-spacing: -.2px;
  margin-bottom: 8px;
}
.card-desc {
  font-size: .875rem;
  color: var(--t2);
  line-height: 1.55;
  flex-grow: 1;
}
.card-link {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  margin-top: 18px;
  font-size: .825rem;
  font-weight: 600;
  color: var(--navy-2);
  transition: color .13s;
}
.card:hover .card-link { color: var(--navy); }

/* =========================================
   8. Updates Section
   ========================================= */
.updates-band {
  background: var(--bg);
  border-top: 1px solid var(--border-2);
  padding: 64px 24px;
}
.updates-inner {
  max-width: 680px;
  margin: 0 auto;
}
.updates-inner h2 {
  font-size: 1.5rem !important;
  font-weight: 700 !important;
  letter-spacing: -.02em !important;
  color: var(--t1) !important;
  margin: 0 0 24px !important;
  text-shadow: none !important;
}
.updates-list {
  list-style: none;
  border: 1px solid var(--border-2);
  border-radius: var(--r-md);
  overflow: hidden;
  background: var(--white);
  box-shadow: var(--s1);
}
.updates-list li {
  padding: 15px 20px;
  font-size: .9rem;
  color: var(--t2);
  border-bottom: 1px solid var(--border-2);
  transition: background .13s;
  line-height: 1.5;
}
.updates-list li:last-child { border-bottom: none; }
.updates-list li:hover { background: var(--gold-pale); color: var(--t1); }
.updates-list li strong { color: var(--navy); font-weight: 600; }
.contact-row {
  margin-top: 18px;
  text-align: center;
  font-size: .85rem;
  color: var(--t3);
}
.contact-row a { color: var(--navy-2); font-weight: 500; text-decoration: none; }
.contact-row a:hover { text-decoration: underline; }

/* =========================================
   9. Doc Layout (Exams / Notes)
      Two-column: sticky sidebar + scrolling main
   ========================================= */
.doc-layout {
  display: grid;
  grid-template-columns: 232px 1fr;
  max-width: 1160px;
  margin: 0 auto;
  padding: 0 24px;
  gap: 0;
  min-height: calc(100vh - var(--nav-h));
  align-items: start;
}

/* ---- Sidebar ---- */
.doc-sidebar {
  position: sticky;
  top: var(--nav-h);
  height: calc(100vh - var(--nav-h));
  overflow-y: auto;
  padding: 28px 20px 40px 0;
  border-right: 1px solid var(--border-2);
  scrollbar-width: thin;
  scrollbar-color: var(--border) transparent;
}
.doc-sidebar::-webkit-scrollbar { width: 4px; }
.doc-sidebar::-webkit-scrollbar-thumb { background: var(--border); border-radius: 4px; }

.sidebar-inner { padding-right: 4px; }

/* Search box in sidebar */
.sidebar-search {
  position: relative;
  margin-bottom: 22px;
}
.sidebar-search .search-icon {
  position: absolute;
  left: 10px;
  top: 50%;
  transform: translateY(-50%);
  width: 14px;
  height: 14px;
  color: var(--t3);
  pointer-events: none;
}
.sidebar-search input {
  width: 100%;
  padding: 8px 10px 8px 30px;
  font-size: .82rem;
  font-family: inherit;
  border: 1px solid var(--border);
  border-radius: var(--r-sm);
  background: var(--bg);
  color: var(--t1);
  outline: none;
  transition: border-color .15s, box-shadow .15s, background .15s;
}
.sidebar-search input:focus {
  border-color: var(--navy-2);
  background: var(--white);
  box-shadow: 0 0 0 3px rgba(46,74,119,.1);
}
.sidebar-search input::placeholder { color: var(--t3); }

.sidebar-heading {
  font-size: .66rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 1.8px;
  color: var(--t3);
  margin-bottom: 8px;
  padding-left: 2px;
}

/* TOC links */
.sidebar-toc {
  display: flex;
  flex-direction: column;
  gap: 1px;
}
.toc-link {
  display: block;
  padding: 6px 10px;
  font-size: .78rem;
  color: var(--t2);
  text-decoration: none;
  border-radius: 6px;
  transition: background .12s, color .12s;
  line-height: 1.4;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}
.toc-link:hover { background: var(--bg); color: var(--t1); }
.toc-link.toc-active {
  background: var(--gold-pale);
  color: var(--navy);
  font-weight: 600;
}
.toc-link.toc-dim { opacity: 0.3; }

/* ---- Main content ---- */
.doc-main {
  padding: 36px 0 80px 36px;
  min-width: 0;
}

/* =========================================
   10. General Headings (doc pages)
   ========================================= */
h1 {
  font-size: 1.9rem;
  font-weight: 700;
  letter-spacing: -.025em;
  color: var(--t1);
  padding-bottom: 14px;
  margin-bottom: 28px;
  border-bottom: 1px solid var(--border-2);
  text-shadow: none;
}

h2 {
  font-size: 1.3rem;
  font-weight: 700;
  color: var(--t1);
  margin-top: 40px;
  margin-bottom: 12px;
  letter-spacing: -.01em;
  text-shadow: none;
}

/* =========================================
   11. Course Cards — h3 + ul (Exams/Notes)
       Styled like an iOS settings panel
   ========================================= */
h3 {
  /* Section header */
  display: flex;
  align-items: center;
  background: var(--white);
  color: var(--t1);
  font-size: .92rem;
  font-weight: 700;
  letter-spacing: -.1px;
  padding: 13px 18px;
  border: 1px solid var(--border-2);
  border-radius: var(--r-md) var(--r-md) 0 0;
  margin-top: 28px;
  margin-bottom: 0;
  scroll-margin-top: calc(var(--nav-h) + 20px);
  position: relative;
  gap: 0;
}
/* Gold pill tag on left */
h3::before {
  content: '';
  display: inline-block;
  width: 3px;
  height: 16px;
  background: var(--gold);
  border-radius: 2px;
  margin-right: 12px;
  flex-shrink: 0;
}

h3 + ul {
  list-style: none;
  background: var(--white);
  border: 1px solid var(--border-2);
  border-top: 1px solid var(--border-2);
  border-radius: 0 0 var(--r-md) var(--r-md);
  padding: 6px 0 8px;
  margin: 0;
  box-shadow: var(--s1);
}

/* Year label row */
h3 + ul > li {
  font-size: .66rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 2px;
  color: var(--t3);
  padding: 10px 18px 5px;
  border-bottom: none;
  border-top: 1px solid var(--border-2);
}
h3 + ul > li:first-child { border-top: none; padding-top: 10px; }

h3 + ul > li > ul {
  list-style: none;
  padding: 0;
}

/* File row */
h3 + ul > li > ul > li {
  border-bottom: 1px solid var(--border-2);
  transition: background .12s;
}
h3 + ul > li > ul > li:last-child { border-bottom: none; }
h3 + ul > li > ul > li:hover { background: var(--gold-pale); }

h3 + ul > li > ul > li a {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 11px 18px;
  text-decoration: none;
  color: var(--navy-2);
  font-size: .875rem;
  font-weight: 500;
  transition: color .12s;
}
h3 + ul > li > ul > li:hover a { color: var(--navy); }

h3 + ul > li > ul > li a::before {
  content: "📄";
  font-size: .85rem;
  opacity: .65;
  flex-shrink: 0;
}
h3 + ul > li > ul > li a::after {
  content: "↓";
  margin-left: auto;
  font-size: .75rem;
  font-weight: 700;
  color: var(--gold);
  opacity: 0;
  transform: translateY(-4px);
  transition: opacity .13s, transform .13s;
}
h3 + ul > li > ul > li:hover a::after { opacity: 1; transform: translateY(0); }

/* =========================================
   12. Standard Page (.std-page)
   ========================================= */
.std-page {
  max-width: 760px;
  margin: 0 auto;
  padding: 0 24px;
}
.std-main { padding: 40px 0 80px; }

/* =========================================
   13. Tables (Activities)
   ========================================= */
table {
  width: 100%;
  border-collapse: collapse;
  margin: 24px 0;
  background: var(--white);
  border-radius: var(--r-md);
  overflow: hidden;
  box-shadow: var(--s1);
  border: 1px solid var(--border-2);
}
thead { background: var(--navy); }
th {
  padding: 12px 16px;
  text-align: left;
  font-weight: 600;
  text-transform: uppercase;
  font-size: .65rem;
  letter-spacing: 1.8px;
  color: rgba(255,255,255,.65);
}
td {
  padding: 12px 16px;
  font-size: .875rem;
  color: var(--t2);
  border-bottom: 1px solid var(--border-2);
}
tr:last-child td { border-bottom: none; }
tbody tr:hover td { background: var(--gold-pale); color: var(--t1); }
td a { color: var(--navy-2); text-decoration: none; font-weight: 500; }
td a:hover { text-decoration: underline; }

/* =========================================
   14. Footer
   ========================================= */
.site-footer {
  background: var(--bg);
  border-top: 1px solid var(--border-2);
  padding: 32px 24px;
}
.footer-inner {
  max-width: 1080px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-wrap: wrap;
  gap: 6px;
  font-size: .8rem;
  color: var(--t3);
}
.footer-brand { font-weight: 700; color: var(--t2); }
.footer-sep { color: var(--border); }

/* =========================================
   15. Scroll-reveal Animation
   ========================================= */
.reveal {
  opacity: 0;
  transform: translateY(22px);
  transition: opacity .5s ease, transform .5s ease;
}
.reveal.revealed { opacity: 1; transform: translateY(0); }
.reveal:nth-child(2) { transition-delay: .07s; }
.reveal:nth-child(3) { transition-delay: .14s; }

/* =========================================
   16. Responsive
   ========================================= */
@media (max-width: 960px) {
  /* Collapse doc layout to single column */
  .doc-layout {
    grid-template-columns: 1fr;
    padding: 0;
    gap: 0;
  }
  .doc-sidebar {
    position: static;
    height: auto;
    overflow: visible;
    padding: 16px 20px 4px;
    border-right: none;
    border-bottom: 1px solid var(--border-2);
    background: var(--bg);
  }
  .sidebar-toc,
  .sidebar-heading { display: none; }
  .doc-main { padding: 24px 20px 60px; }

  /* Nav */
  .nav-links { display: none; }
  .nav-hamburger { display: flex; }
}

@media (max-width: 640px) {
  .hero { padding: 72px 20px 56px; }
  .hero-cta { flex-direction: column; }
  .btn-primary, .btn-ghost { width: 100%; max-width: 300px; justify-content: center; }
  .stats-bar { flex-wrap: wrap; }
  .stat { padding: 20px 28px; border-right: none; border-bottom: 1px solid var(--border); }
  .stat:last-child { border-bottom: none; }
  .home-section { padding: 52px 20px; }
  .updates-band { padding: 44px 20px; }
  table { display: block; overflow-x: auto; white-space: nowrap; }
}