/* ══════════════════════════════════════════
   OSEI Lab — Shared Stylesheet
   Style: Teal header · clean white · mono tags
   ══════════════════════════════════════════ */

@import url('https://fonts.googleapis.com/css2?family=JetBrains+Mono:wght@400;700&family=Pretendard:wght@300;400;600;800&display=swap');

:root {
  --brand-teal:       #15a198;
  --brand-teal-dark:  #10857d;
  --brand-teal-light: #e0f2f1;
  --bg-main:    #ffffff;
  --bg-alt:     #f8fafc;
  --bg-card:    #ffffff;
  --text-heading: #0f172a;
  --text-main:    #334155;
  --text-muted:   #64748b;
  --border-color: #e2e8f0;
  --shadow-sm:    0 4px 6px -1px rgba(0,0,0,0.05);
  --shadow-md:    0 10px 25px -5px rgba(0,0,0,0.05);
  --shadow-hover: 0 20px 40px -5px rgba(21,161,152,0.15);
  --font-sans:    'Pretendard', sans-serif;
  --font-mono:    'JetBrains Mono', monospace;
  --nav-h: 90px;
}

*,*::before,*::after { margin:0; padding:0; box-sizing:border-box; }
html { scroll-behavior: smooth; }
body {
  font-family: var(--font-sans);
  background: var(--bg-main);
  color: var(--text-main);
  line-height: 1.6;
  overflow-x: hidden;
}
a { text-decoration: none; color: inherit; }
ul { list-style: none; }

/* ── Layout ── */
.container { max-width: 1200px; margin: 0 auto; padding: 0 2rem; }
.section { padding: 8rem 0; position: relative; }
.bg-alt { background-color: var(--bg-alt); }

/* ── Section labels ── */
.section-tag {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 0.85rem;
  color: var(--brand-teal);
  text-transform: uppercase;
  letter-spacing: 2px;
  margin-bottom: 1rem;
  font-weight: 700;
}
.section-tag::before { content: '/> '; }

.section-title {
  font-size: 2.5rem; font-weight: 800;
  margin-bottom: 3rem;
  color: var(--text-heading);
  letter-spacing: -0.02em;
}

/* ── Reveal animation ── */
.reveal {
  opacity: 0; transform: translateY(30px);
  transition: all 0.8s cubic-bezier(0.16,1,0.3,1);
}
.reveal.visible { opacity: 1; transform: translateY(0); }

/* ══════════════
   HEADER / NAV
   ══════════════ */
header {
  position: fixed; top: 0; width: 100%; z-index: 100;
  background: var(--brand-teal);
  box-shadow: 0 2px 10px rgba(0,0,0,0.1);
  transition: padding 0.3s ease, box-shadow 0.3s ease;
}
.nav-container {
  display: flex; justify-content: space-between; align-items: center;
  height: var(--nav-h); max-width: 1200px; margin: 0 auto; padding: 0 2rem;
  position: relative;
}
.logo { display: flex; align-items: center; }
.logo-text {
  font-family: var(--font-mono); font-size: 1.3rem; font-weight: 700;
  color: #fff; letter-spacing: 1px;
}
.logo-sub {
  font-size: 0.7rem; color: rgba(255,255,255,0.75);
  display: block; letter-spacing: 0.5px; margin-top: 2px;
}
.custom-logo {
  height: 70px; width: auto; object-fit: contain;
  mix-blend-mode: multiply; transition: height 0.3s ease;
}

.nav-links {
  display: flex; gap: 2.5rem;
  font-size: 0.95rem; font-weight: 600;
  color: rgba(255,255,255,0.9);
}
.nav-links a { transition: color 0.2s; }
.nav-links a:hover,
.nav-links a.active {
  color: #ffffff;
  text-decoration: underline;
  text-underline-offset: 4px;
}

/* Mobile menu btn */
.mobile-menu-btn {
  display: none; background: none; border: none;
  cursor: pointer; flex-direction: column; gap: 5px;
  padding: 10px; z-index: 101;
}
.mobile-menu-btn span {
  display: block; width: 25px; height: 3px;
  background: #ffffff; border-radius: 2px; transition: 0.3s;
}

/* ══════════
   PAGE HERO (sub-pages)
   ══════════ */
.page-hero {
  background-color: var(--brand-teal);
  padding-top: calc(var(--nav-h) + 5rem);
  padding-bottom: 5rem;
  position: relative; overflow: hidden;
}
.page-hero-bg {
  position: absolute; inset: 0;
  background-image: radial-gradient(rgba(255,255,255,0.15) 2px, transparent 2px);
  background-size: 30px 30px; opacity: 0.5;
}
.page-hero-grad {
  position: absolute; inset: 0;
  background: linear-gradient(135deg, transparent 0%, rgba(0,0,0,0.08) 100%);
}
.page-hero-inner {
  max-width: 1200px; margin: 0 auto; padding: 0 2rem;
  position: relative; z-index: 1; color: #fff;
}
.page-hero-inner .section-tag { color: rgba(255,255,255,0.8); }
.page-hero-title {
  font-size: clamp(2rem,4.5vw,3.5rem);
  font-weight: 800; color: #fff;
  letter-spacing: -0.02em; line-height: 1.2;
  margin-bottom: 1rem;
}
.page-hero-desc {
  font-size: 1.1rem; color: rgba(255,255,255,0.85);
  max-width: 640px; line-height: 1.8; font-weight: 300;
}

/* ══════════
   FOOTER
   ══════════ */
footer {
  background: #0f172a;
  padding: 5rem 0 2rem;
  color: rgba(255,255,255,0.7);
  font-size: 0.95rem;
}
.footer-grid {
  display: grid; grid-template-columns: 1fr 1.5fr;
  gap: 4rem; margin-bottom: 4rem;
  border-bottom: 1px solid rgba(255,255,255,0.1);
  padding-bottom: 4rem;
}
.footer-logo-area { display: flex; flex-direction: column; align-items: flex-start; }
.footer-logo { height: 70px; margin-bottom: 1.5rem; filter: invert(1); opacity: 0.9; }
.footer-title {
  font-family: var(--font-mono); font-size: 1.3rem;
  font-weight: 700; color: #fff; margin-bottom: 0.5rem;
}
.contact-area h4 {
  font-size: 1.2rem; font-weight: 700; color: #fff; margin-bottom: 1.5rem;
  font-family: var(--font-mono); letter-spacing: 1px; text-transform: uppercase;
}
.contact-list { display: flex; flex-direction: column; gap: 1rem; }
.contact-item { display: flex; gap: 1rem; align-items: flex-start; }
.contact-icon { font-weight: 700; color: var(--brand-teal); width: 24px; }
.copyright {
  text-align: center; font-size: 0.9rem; color: rgba(255,255,255,0.5);
}

/* ══════════════
   RESPONSIVE
   ══════════════ */
@media (max-width: 900px) {
  .footer-grid { grid-template-columns: 1fr; gap: 2.5rem; padding-bottom: 2.5rem; margin-bottom: 2.5rem; }
}
@media (max-width: 768px) {
  :root { --nav-h: 70px; }
  .nav-container { padding: 0 1.2rem; }
  .custom-logo { height: 50px; }
  .mobile-menu-btn { display: flex; }
  .nav-links {
    display: none; flex-direction: column;
    position: absolute; top: var(--nav-h); left: 0; width: 100%;
    background: var(--brand-teal);
    padding: 1.5rem 2rem; gap: 1.5rem;
    border-top: 1px solid rgba(255,255,255,0.1);
    box-shadow: 0 10px 15px rgba(0,0,0,0.1);
  }
  .nav-links.active { display: flex; }
  .container { padding: 0 1.5rem; }
  .section { padding: 5rem 0; }
  .section-title { font-size: 2rem; margin-bottom: 2rem; }
  .page-hero { padding-top: calc(var(--nav-h) + 3rem); padding-bottom: 3rem; }
}