/* Mathematical Alphabet Labs — shared stylesheet
   Structure: Anthropic-style nav dropdowns, flat sections, hairline dividers.
   Theme: exact blue palette + logo from the Mathematical Alphabet reference site. */

:root{
  --paper: #f2f7fb;
  --ink: #0a1828;
  --ink-soft: #1e3347;
  --muted: #4a6278;
  --hair: #c8dcea;

  --navy: #013766;
  --blue: #2c5b85;
  --blue-mid: #567f9f;
  --blue-light: #81a3bf;
  --blue-pale: #afc4d5;
  --pale-tint: #d9e7f2;

  --serif: "Source Serif 4", "Cambria", Georgia, serif;
  --sans: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;

  --accent: var(--navy);
  --accent-deep: var(--blue);
  --accent-tint: var(--pale-tint);
}

*{ box-sizing:border-box; }
html{ scroll-behavior:smooth; }
body{
  margin:0;
  background:var(--paper);
  color:var(--ink);
  font-family:var(--sans);
  font-size:16px;
  line-height:1.6;
  -webkit-font-smoothing:antialiased;
}
img{ max-width:100%; display:block; }
a{ color:inherit; text-decoration:none; }
h1,h2,h3{ font-family:var(--sans); font-weight:800; letter-spacing:-.02em; line-height:1.04; margin:0; color:var(--ink); }
h4{ font-family:var(--serif); font-weight:700; line-height:1.25; margin:0; color:var(--ink); }
p{ margin:0; }
.container{ max-width:1180px; margin:0 auto; padding:0 32px; }
.eyebrow{
  font-family:var(--sans); font-size:28px; font-weight:800; letter-spacing:-.01em;
  color:var(--accent); margin:0 0 8px;
}
.section{ padding:88px 0; }
.section--tight{ padding:64px 0; }
.muted{ color:var(--muted); }
.rule{ border:none; border-top:1px solid var(--hair); margin:0; }

/* buttons */
.btn{
  display:inline-flex; align-items:center; gap:8px;
  padding:12px 24px; border-radius:999px; font-family:var(--sans);
  font-size:14.5px; font-weight:600; border:1.5px solid transparent;
  cursor:pointer; transition:all .18s ease;
}
.btn-primary{ background:var(--navy); color:#fff; }
.btn-primary:hover{ background:var(--blue); }
.btn-ghost{ background:transparent; color:var(--ink); border-color:var(--hair); }
.btn-ghost:hover{ border-color:var(--accent); color:var(--accent); }
.btn-arrow{ transition:transform .18s ease; }
.btn:hover .btn-arrow{ transform:translateX(3px); }

/* nav */
.nav{
  position:sticky; top:0; z-index:50; background:rgba(242,247,251,.92);
  backdrop-filter:blur(10px); border-bottom:1px solid var(--hair);
}
.nav .container{
  display:flex; align-items:center; justify-content:space-between; height:80px;
  max-width:1340px; gap:20px;
}
.nav-brand{
  display:flex; align-items:center; gap:12px; font-family:var(--serif); font-weight:700;
  font-size:19px; color:var(--navy); letter-spacing:-.01em; white-space:nowrap; flex-shrink:0;
}
.nav-brand .accent-letter{ color:var(--blue-mid); }
.nav-links{ display:flex; align-items:center; gap:18px; position:relative; flex-shrink:1; }
.nav-item{ position:relative; display:flex; align-items:center; }
.nav-item > button.nav-link, .nav-item > a.nav-link{
  background:none; border:none; font:inherit; cursor:pointer;
  font-size:13.5px; font-weight:500; color:var(--ink); padding:6px 0; white-space:nowrap;
  display:flex; align-items:center; gap:5px; border-bottom:2px solid transparent;
  font-family:var(--sans);
}
.nav-item > button.nav-link:hover, .nav-item > a.nav-link:hover{ color:var(--accent); border-color:var(--accent); }
.nav-item .caret{
  display:inline-block; width:0; height:0; margin-top:2px;
  border-left:3.5px solid transparent; border-right:3.5px solid transparent;
  border-top:4.5px solid currentColor; transition:transform .15s ease;
}
.nav-item:hover .caret{ transform:rotate(180deg); }
.dropdown{
  position:absolute; top:calc(100% + 14px); left:50%; transform:translateX(-50%) translateY(-6px);
  background:#fff; border:1px solid var(--hair); border-radius:14px; padding:10px;
  min-width:220px; box-shadow:0 20px 40px rgba(10,24,40,.12);
  opacity:0; pointer-events:none; transition:opacity .15s ease, transform .15s ease;
  z-index:60;
}
.nav-item:hover .dropdown, .nav-item.open .dropdown{ opacity:1; pointer-events:auto; transform:translateX(-50%) translateY(0); }
.dropdown a{ display:block; padding:10px 14px; border-radius:8px; font-size:14px; color:var(--ink); white-space:normal; }
.dropdown a:hover{ background:var(--accent-tint); color:var(--accent); }
.dropdown a .sub{ display:block; font-size:12px; color:var(--muted); margin-top:2px; font-family:var(--sans); }
.nav-actions{ display:flex; align-items:center; gap:10px; flex-shrink:0; }
.nav-cta{ display:flex; align-items:center; background:var(--navy); border-radius:999px; overflow:hidden; white-space:nowrap; }
.nav-cta span{ padding:10px 16px; color:#fff; font-size:13.5px; font-weight:600; white-space:nowrap; }
.nav-cta .chev{
  display:flex; align-items:center; justify-content:center; padding:0 12px; align-self:stretch;
  border-left:1px solid rgba(255,255,255,.22);
}
.nav-cta .chev::before{
  content:""; display:inline-block; width:0; height:0;
  border-left:3.5px solid transparent; border-right:3.5px solid transparent;
  border-top:4.5px solid #fff;
}
.nav-cta:hover{ background:var(--blue); }
.btn-ghost-accent{
  padding:9px 16px; border-radius:999px; border:1.5px solid var(--accent); color:var(--accent);
  font-size:13px; font-weight:600; font-family:var(--sans); transition:all .18s ease; white-space:nowrap;
}
.btn-ghost-accent:hover{ background:var(--accent); color:#fff; }
.nav-toggle{ display:none; }

/* logo: rotating globe with pillar glyphs inside */
.logo-globe{
  width:52px; height:52px; border-radius:50%; flex-shrink:0; position:relative; overflow:hidden;
  background:radial-gradient(circle at 38% 36%, var(--blue-light) 0%, var(--blue) 42%, var(--navy) 76%, #051225 100%);
  box-shadow:inset -4px -3px 10px rgba(5,18,37,.55), inset 3px 2px 8px rgba(175,196,213,.2);
}
.logo-globe::before{
  content:""; position:absolute; inset:0; border-radius:50%; pointer-events:none;
  background:radial-gradient(circle 16px at 50% 50%, rgba(255,255,255,.6), transparent 70%);
  background-repeat:no-repeat; mix-blend-mode:screen;
  animation:globeSpin 3s linear infinite;
}
@keyframes globeSpin{
  0%{   background-position:18% 22%; }
  25%{  background-position:78% 18%; }
  50%{  background-position:80% 74%; }
  75%{  background-position:20% 78%; }
  100%{ background-position:18% 22%; }
}
.logo-globe span{ position:absolute; font-family:var(--serif); font-weight:700; color:rgba(255,255,255,.92); z-index:1; }
.logo-globe .g1{ font-size:17px; top:7px; left:9px; animation:gOrb1 3s ease-in-out infinite; }
.logo-globe .g2{ font-size:19px; font-weight:900; bottom:7px; right:6px; color:var(--pale-tint); animation:gOrb2 3.4s ease-in-out infinite; }
.logo-globe .g3{ font-size:13px; font-weight:900; top:9px; right:8px; line-height:1; color:var(--blue-pale); animation:gOrb3 2.8s ease-in-out infinite; }
.logo-globe .g3 small{ font-size:7px; vertical-align:middle; color:var(--blue-pale); }
@keyframes gOrb1{ 0%,100%{ transform:translate(0,0); } 50%{ transform:translate(2px,-2px); } }
@keyframes gOrb2{ 0%,100%{ transform:translate(0,0); } 50%{ transform:translate(-2px,2px); } }
@keyframes gOrb3{ 0%,100%{ transform:translate(0,0); } 50%{ transform:translate(2px,2px); } }

/* hero: medium blue density */
.hero{
  padding:80px 0 56px; position:relative; overflow:hidden;
  background:linear-gradient(155deg, var(--blue) 0%, var(--blue-mid) 100%);
}
.hero::before{
  content:""; position:absolute; inset:0; z-index:0;
  background:radial-gradient(circle at 82% 15%, rgba(13,32,56,.22), transparent 55%),
             radial-gradient(circle at 10% 80%, rgba(217,231,242,.22), transparent 50%);
}
.hero-grid{ display:grid; grid-template-columns:.95fr 1.05fr; gap:56px; align-items:start; position:relative; z-index:1; }
.hero h1{ font-size:64px; color:#fff; }
.hero .lede{ font-family:var(--serif); font-size:21px; color:#fff; max-width:520px; line-height:1.5; }
.hero .hero-mission{ font-family:var(--sans); font-size:16px; color:#E4EBF1; max-width:520px; line-height:1.6; margin-top:16px; }
.hero .links{ margin-top:18px; font-family:var(--sans); font-size:14px; color:#E4EBF1; }
.hero .links a{ color:#fff; border-bottom:1px solid rgba(255,255,255,.5); font-weight:600; }
.hero .links a:hover{ border-color:#fff; }
.hero-cta{ display:flex; gap:14px; margin-top:30px; }

/* dynamic math-symbol background: clearly moving, both axes */
.symbol-field{ position:absolute; inset:0; overflow:hidden; pointer-events:none; z-index:0; }
.symbol-field span{
  position:absolute; font-family:var(--serif); color:rgba(255,255,255,.5); opacity:.55;
  animation:drift 3.5s ease-in-out infinite;
}
@keyframes drift{
  0%{   transform:translate(0,0) rotate(0deg); }
  25%{  transform:translate(14px,-22px) rotate(8deg); }
  50%{  transform:translate(-10px,-38px) rotate(-6deg); }
  75%{  transform:translate(-18px,-14px) rotate(10deg); }
  100%{ transform:translate(0,0) rotate(0deg); }
}

/* flat grid section (Anthropic team-cards look) */
.flat-grid{ display:grid; grid-template-columns:repeat(3,1fr); gap:40px; padding-top:44px; }
.flat-grid.cols-4{ grid-template-columns:repeat(4,1fr); }
.flat-col h4{ font-size:19px; margin-bottom:10px; }
.flat-col p{ font-family:var(--serif); font-size:15px; color:var(--ink-soft); line-height:1.6; }
.flat-col{ transition:opacity .15s ease; }
a.flat-col:hover{ opacity:.6; }
.flat-col .role{ font-family:var(--sans); font-size:11.5px; font-weight:700; letter-spacing:.08em; text-transform:uppercase; color:var(--accent); margin-bottom:10px; display:block; }
.flat-col .arrow-link{ display:inline-block; margin-top:14px; font-family:var(--sans); font-size:13.5px; font-weight:600; color:var(--accent); }

/* two column section */
.split{ display:grid; grid-template-columns:1fr 1fr; gap:64px; align-items:center; }

/* quote rotator */
.quote-wrap{ position:relative; min-height:150px; }
.quote-slide{
  position:absolute; inset:0; opacity:0; transition:opacity .9s ease;
  display:flex; flex-direction:column; justify-content:center;
}
.quote-slide.active{ opacity:1; position:relative; }
.quote-slide blockquote{
  font-family:var(--serif); font-size:26px; font-weight:500; line-height:1.45; margin:0; max-width:780px;
}
.quote-slide .quote-attrib{ margin-top:16px; font-size:12.5px; font-weight:700; letter-spacing:.1em; text-transform:uppercase; color:var(--accent); }
.quote-dots{ display:flex; gap:8px; margin-top:32px; }
.quote-dots span{ width:7px; height:7px; border-radius:50%; background:var(--hair); transition:background .2s ease; }
.quote-dots span.active{ background:var(--accent); }

/* stub notes (Learn / News) */
.stub-note{
  font-family:var(--serif); font-size:14px; color:var(--muted); font-style:italic;
  border-top:1px dashed var(--hair); padding-top:14px; margin-top:14px;
}

/* section theming: distinct blue gradient per pillar */
.tab-anchor{ scroll-margin-top:96px; }
.section-principia{ background:linear-gradient(160deg, var(--pale-tint) 0%, var(--paper) 65%); }
.section-lambda{ --accent:var(--pale-tint); background:linear-gradient(160deg, var(--ink) 0%, var(--blue) 100%); color:#EAF1F8; }
.section-lambda h2, .section-lambda h3{ color:#fff; }
.section-lambda p{ color:#C7D6E4; }
.section-lambda .flat-col h4{ color:#fff; }
.section-lambda .flat-col p{ color:#C7D6E4; }
.section-lemma{ --accent:var(--pale-tint); background:linear-gradient(160deg, var(--blue) 0%, var(--blue-light) 100%); color:#F2F6F9; }
.section-lemma h2, .section-lemma h3{ color:#fff; }
.section-lemma p{ color:#E4EBF1; }
.section-lemma .flat-col h4{ color:#fff; }
.section-lemma .flat-col p{ color:#E4EBF1; }
.section--gradient{ background:linear-gradient(150deg, var(--navy) 0%, var(--blue) 55%, var(--blue-mid) 100%); color:#EAF1F8; position:relative; }
.section--gradient h2, .section--gradient h3{ color:#fff; }
.section--gradient .muted{ color:#C7D6E4; }

/* Brookings-style research block (unchanged: approved as-is) */
.brookings-head{ display:block; }
.brookings-head .brookings-desc{ margin-top:14px; max-width:760px; }
.brookings-title{ font-family:var(--sans); font-weight:700; letter-spacing:-.01em; font-size:20px; color:var(--ink-soft); }
.brookings-desc p{ font-family:var(--serif); font-size:15px; color:var(--ink-soft); line-height:1.65; }
.jump-links{ display:flex; gap:30px; margin:24px 0 6px; flex-wrap:wrap; }
.jump-links a{ color:var(--accent); font-size:14px; font-weight:600; }
.jump-links a::before{ content:"↓ "; }
.brookings-grid{ display:grid; grid-template-columns:repeat(3,1fr); gap:30px; margin-top:10px; }
.brookings-col{ border-top:1px dotted var(--hair); padding-top:18px; }
.brookings-col h4{ font-size:16.5px; margin-bottom:14px; }
.brookings-col p{ font-family:var(--serif); font-size:13.5px; color:var(--ink-soft); }
.brookings-tile{
  border-radius:10px; height:160px; position:relative; overflow:hidden;
  display:flex; align-items:flex-end; padding:16px; margin-bottom:14px;
}
.tile-label{ color:#fff; font-family:var(--serif); font-weight:700; font-size:15.5px; display:flex; flex-direction:column; }
.tile-label small{ font-family:var(--sans); font-weight:500; font-size:10.5px; letter-spacing:.06em; text-transform:uppercase; color:rgba(255,255,255,.8); margin-top:5px; }
.grad-tile-1{ background:linear-gradient(135deg, var(--ink), var(--navy) 55%, var(--blue)); }
.grad-tile-2{ background:linear-gradient(135deg, var(--navy), var(--blue) 55%, var(--blue-light)); }
.grad-tile-3{ background:linear-gradient(135deg, var(--blue), var(--blue-light) 55%, var(--blue-pale)); }

/* Academy / donate */
.donate-banner{
  margin-top:40px; border-radius:16px; padding:32px;
  background:linear-gradient(120deg, var(--pale-tint), var(--paper));
  border:1px solid var(--hair);
  display:flex; align-items:center; justify-content:space-between; gap:24px; flex-wrap:wrap;
}
.donate-banner h3{ font-size:20px; font-family:var(--serif); }

/* Engagements: trusted-by wordmark strip */
.engagements-strip{
  display:flex; flex-wrap:wrap; gap:0; margin-top:36px; border-top:1px solid var(--hair); padding-top:28px;
}
.engagements-strip span{
  font-family:var(--serif); font-size:15px; font-weight:600; color:var(--ink-soft);
  padding:8px 26px; border-right:1px solid var(--hair);
}
.engagements-strip span:last-child{ border-right:none; }

/* footer */
.footer{ background:var(--ink); color:#EAF1F8; padding:64px 0 28px; }
.footer-grid{ display:grid; grid-template-columns:1.4fr repeat(4,1fr); gap:32px; }
.footer-brand{ font-family:var(--serif); font-size:19px; font-weight:700; color:#fff; }
.footer-tag{ margin-top:12px; color:#9FB2C4; font-size:13.5px; max-width:260px; font-family:var(--serif); }
.footer-col h5{ font-size:12px; font-weight:700; letter-spacing:.08em; text-transform:uppercase; color:var(--blue-pale); margin-bottom:16px; }
.footer-col a{ display:block; font-size:14px; color:#CBDAE7; padding:5px 0; }
.footer-col a:hover{ color:#fff; }
.footer-bottom{ margin-top:48px; padding-top:22px; border-top:1px solid rgba(255,255,255,.12); display:flex; justify-content:space-between; color:#8FA2B4; font-size:13px; }

/* utility */
.center{ text-align:center; }
.mt-8{ margin-top:8px; } .mt-16{ margin-top:16px; } .mt-24{ margin-top:24px; } .mt-40{ margin-top:40px; }
.max-640{ max-width:640px; } .max-720{ max-width:720px; margin-left:auto; margin-right:auto; }

/* mobile */
@media (max-width: 920px){
  .hero-grid, .split{ grid-template-columns:1fr; }
  .flat-grid, .flat-grid.cols-4, .brookings-grid{ grid-template-columns:1fr; gap:32px; }
  .footer-grid{ grid-template-columns:1fr 1fr; }
  .hero h1{ font-size:40px; }
  .nav-links{ display:none; }
  .section{ padding:56px 0; }
  .nav-brand{ font-size:18px; }
  .engagements-strip span{ border-right:none; padding:6px 0; width:50%; }
}



/* contact phone numbers */
.contact-phones{
  display:flex; gap:28px; justify-content:center; flex-wrap:wrap;
  font-family:var(--serif); font-size:15px; color:var(--ink-soft);
}
.contact-phones a{ border-bottom:1px solid transparent; }
.contact-phones a:hover{ color:var(--accent); border-color:var(--accent); }

/* Illustrated section banners (stylistic graphics in place of photography) */
.section-banner{
  width:100%; height:180px; border-radius:16px; overflow:hidden; position:relative;
  margin:32px 0 8px;
}
.section-banner svg{ width:100%; height:100%; display:block; }
.section-banner .banner-caption{
  position:absolute; left:20px; bottom:16px; color:#fff; font-family:var(--serif);
  font-weight:700; font-size:15px; z-index:2;
}
.section-banner .banner-caption small{
  display:block; font-family:var(--sans); font-weight:500; font-size:10.5px;
  letter-spacing:.06em; text-transform:uppercase; color:rgba(255,255,255,.75); margin-top:4px;
}