*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --bg:     #0c0c0c;
  --border: #222222;
  --text:   #c8c8c8;
  --dim:    #585858;
  --cyan:   #00c8ff;
  --purple: #a855f7;
  --pink:   #ff2d78;
  --gold:   #f5a623;
  --nav-h:  60px;
}

html { scroll-behavior: smooth; }

body {
  font-family: 'Segoe UI', system-ui, sans-serif;
  background: var(--bg);
  color: var(--text);
  overflow-x: hidden;
}

::-webkit-scrollbar { width: 3px; }
::-webkit-scrollbar-track { background: var(--bg); }
::-webkit-scrollbar-thumb { background: #333; border-radius: 2px; }

nav {
  position: fixed; top: 0; left: 0; right: 0; z-index: 100;
  height: var(--nav-h);
  display: flex; align-items: center; justify-content: space-between;
  padding: 0 3rem;
  background: rgba(12,12,12,0.92);
  backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--border);
}

.nav-logo {
  font-size: .72rem; font-weight: 800; letter-spacing: .28em;
  color: #fff; text-decoration: none; text-transform: uppercase;
}

.nav-links { display: flex; gap: 2.5rem; list-style: none; }

.nav-links a {
  font-size: .68rem; letter-spacing: .15em; text-transform: uppercase;
  color: var(--dim); text-decoration: none; transition: color .2s;
}
.nav-links a:hover,
.nav-links a.active { color: #fff; }

#hero {
  min-height: 100vh;
  display: flex; flex-direction: column;
  padding-top: var(--nav-h);
  border-bottom: 1px solid var(--border);
  background:
    radial-gradient(ellipse 55% 55% at 0% 100%, rgba(0,200,255,0.18) 0%, transparent 60%),
    radial-gradient(ellipse 45% 50% at 100% 0%, rgba(168,85,247,0.15) 0%, transparent 60%),
    radial-gradient(ellipse 40% 45% at 100% 100%, rgba(255,45,120,0.12) 0%, transparent 55%),
    radial-gradient(ellipse 40% 45% at 0% 0%, rgba(245,166,35,0.10) 0%, transparent 55%),
    radial-gradient(circle, rgba(255,255,255,0.035) 1px, transparent 1px) 0 0 / 24px 24px,
    var(--bg);
}

.hero-main {
  flex: 1;
  display: grid; grid-template-columns: 1fr 1fr;
  align-items: center;
  padding: 3rem 3rem 3rem;
  gap: 4rem;
  border-bottom: 1px solid var(--border);
}

.hero-eyebrow {
  font-size: .68rem; letter-spacing: .3em; text-transform: uppercase;
  color: var(--cyan); margin-bottom: 1.6rem;
  animation: fadeUp .7s ease both;
}

.hero-title {
  font-size: clamp(4.5rem, 10vw, 9rem);
  font-weight: 900; line-height: .85; letter-spacing: -.05em;
  text-transform: uppercase;
  background: linear-gradient(135deg, #ffffff 0%, var(--cyan) 30%, var(--purple) 55%, var(--pink) 78%, var(--gold) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  animation: fadeUp .8s .05s ease both;
}

.hero-authors {
  margin-top: 1.8rem;
  font-size: .72rem; letter-spacing: .18em; text-transform: uppercase;
  color: var(--dim);
  animation: fadeUp .8s .1s ease both;
}

.hero-rule {
  width: 100%; height: 1px; background: var(--border); margin-bottom: 2rem;
  animation: fadeUp .8s .12s ease both;
}

.hero-sub {
  color: var(--dim); font-size: .9rem; line-height: 1.9;
  margin-bottom: 2.5rem;
  animation: fadeUp .8s .16s ease both;
}

.btn {
  display: inline-flex; align-items: center; gap: .5rem;
  padding: .7rem 1.6rem; border-radius: 1px;
  font-size: .68rem; font-weight: 700; letter-spacing: .2em; text-transform: uppercase;
  text-decoration: none; border: 1px solid var(--border);
  background: transparent; color: var(--text); cursor: pointer;
  transition: background .2s, color .2s, border-color .2s;
  animation: fadeUp .8s .2s ease both;
}
.btn:hover { background: #fff; color: var(--bg); border-color: #fff; }
.btn::after { content: '→'; }

.challenge-index {
  display: grid; grid-template-columns: repeat(4, 1fr);
}

.index-item {
  display: flex; align-items: center; gap: .75rem;
  padding: 1.2rem 2rem;
  border-right: 1px solid var(--border);
  text-decoration: none;
  transition: background .2s;
  animation: fadeUp .8s .25s ease both;
}
.index-item:last-child { border-right: none; }
.index-item:hover { background: rgba(255,255,255,0.03); }

.index-dot { width: 8px; height: 8px; border-radius: 50%; flex-shrink: 0; }
.dot-cyan   { background: var(--cyan); }
.dot-purple { background: var(--purple); }
.dot-pink   { background: var(--pink); }
.dot-gold   { background: var(--gold); }
.index-num { font-size: .62rem; letter-spacing: .18em; color: var(--dim); }
.index-name { font-size: .75rem; font-weight: 600; color: var(--text); flex: 1; }
.index-arrow { font-size: .75rem; color: var(--dim); margin-left: auto; }

#challenges { position: relative; }

.project-section {
  border-bottom: 1px solid var(--border);
  overflow: clip;
}

.section-banner {
  display: flex; align-items: center; gap: 2.5rem;
  padding: 2.5rem 3rem;
  background: var(--accent);
  position: relative; overflow: hidden;
}

.banner-num {
  font-size: clamp(5rem, 9vw, 8rem);
  font-weight: 900; line-height: 1; letter-spacing: -.05em;
  color: rgba(0,0,0,0.15); flex-shrink: 0;
  user-select: none;
}

.banner-content { flex: 1; }

.banner-tag {
  display: block; font-size: .63rem; letter-spacing: .22em;
  text-transform: uppercase; margin-bottom: .55rem; opacity: .65;
}

.banner-title {
  font-size: clamp(1.8rem, 3.5vw, 3rem);
  font-weight: 800; letter-spacing: -.03em; line-height: 1.05;
}

.project-grid {
  display: grid; grid-template-columns: 1fr 1fr; align-items: start;
}

.video-col { border-right: 1px solid var(--border); }

.project-section:nth-child(2) .video-col,
.project-section:nth-child(4) .video-col {
  border-right: none;
  border-left: 1px solid var(--border);
}

.video-frame {
  position: relative;
  padding: 1.4rem 1.4rem 0;
}

.video-frame::before,
.video-frame::after {
  content: '';
  position: absolute;
  width: 20px; height: 20px;
  pointer-events: none; z-index: 2;
  opacity: .8;
}
.video-frame::before {
  top: .6rem; left: .6rem;
  border-top: 2px solid var(--accent);
  border-left: 2px solid var(--accent);
}
.video-frame::after {
  bottom: .6rem; right: .6rem;
  border-bottom: 2px solid var(--accent);
  border-right: 2px solid var(--accent);
}

.video-wrap {
  position: relative;
  aspect-ratio: 16/9; background: #000; overflow: hidden;
  outline: 1px solid rgba(255,255,255,0.07);
}
.video-wrap video { width: 100%; height: 100%; object-fit: cover; display: block; }

.video-badge {
  position: absolute;
  top: .65rem; right: .65rem;
  background: rgba(0,0,0,0.62);
  color: var(--accent);
  font-size: .55rem; letter-spacing: .18em; text-transform: uppercase;
  padding: .25rem .6rem;
  backdrop-filter: blur(6px);
  pointer-events: none; z-index: 3;
}

.video-label {
  display: flex; justify-content: space-between; align-items: center;
  padding: .72rem 1.4rem;
  background: var(--accent);
  color: var(--banner-text);
  font-size: .6rem; letter-spacing: .18em; text-transform: uppercase; font-weight: 700;
}

.text-col { padding: 2.5rem 3rem; }

.desc-item {
  display: flex; gap: 1.2rem;
  padding: 1.1rem 0;
  border-bottom: 1px solid var(--border);
}
.desc-item:first-child { padding-top: 0; }

.desc-idx {
  font-size: .58rem; font-weight: 800; letter-spacing: .12em;
  color: var(--accent); flex-shrink: 0; padding-top: .15rem;
  min-width: 1.6rem;
}

.desc-label {
  display: block; font-size: .62rem; letter-spacing: .2em;
  text-transform: uppercase; font-weight: 700;
  color: var(--accent); margin-bottom: .35rem;
}

.desc-text {
  font-size: .875rem; line-height: 1.85; color: var(--dim);
}

.project-chips {
  display: flex; flex-wrap: wrap; gap: .4rem;
  padding-top: 1.6rem; margin-top: .2rem;
}

.chip {
  font-size: .65rem; letter-spacing: .12em; text-transform: uppercase;
  padding: .35rem .8rem; border-radius: 1px;
  border: 1px solid var(--border); color: var(--dim); background: transparent;
  transition: background .18s, color .18s, border-color .18s;
}
.chip a { color: inherit; text-decoration: none; }
.chip:hover { background: var(--accent); border-color: var(--accent); color: #000; }
.chip:hover a { color: #000; }

.project-section:nth-child(1) { --accent: var(--cyan);   --banner-text: #080808; }
.project-section:nth-child(2) { --accent: var(--purple); --banner-text: #ffffff;  }
.project-section:nth-child(3) { --accent: var(--pink);   --banner-text: #ffffff;  }
.project-section:nth-child(4) { --accent: var(--gold);   --banner-text: #080808; }

.section-banner { color: var(--banner-text); }

.project-section:nth-child(1) .desc-item,
.project-section:nth-child(1) .video-col { border-color: #004d6a; }

.project-section:nth-child(2) .desc-item,
.project-section:nth-child(2) .video-col { border-color: #2e1a50; }

.project-section:nth-child(3) .desc-item,
.project-section:nth-child(3) .video-col { border-color: #50003a; }

.project-section:nth-child(4) .desc-item,
.project-section:nth-child(4) .video-col { border-color: #483400; }

footer {
  padding: 1.1rem 3rem;
  border-top: 1px solid var(--border);
  background: var(--bg);
  text-align: center;
}

.footer-copy {
  font-size: .62rem; letter-spacing: .15em; text-transform: uppercase;
  color: var(--dim);
}

.slide-left {
  transform: translateX(-110vw); opacity: 0;
  transition: transform 1.05s cubic-bezier(.16,1,.3,1), opacity .7s ease;
}
.slide-right {
  transform: translateX(110vw); opacity: 0;
  transition: transform 1.05s cubic-bezier(.16,1,.3,1), opacity .7s ease;
}
.fade-in { opacity: 0; transition: opacity .9s ease; }
.slide-up {
  transform: translateY(36px); opacity: 0;
  transition: transform .9s cubic-bezier(.22,1,.36,1), opacity .9s ease;
}
.slide-left.visible, .slide-right.visible,
.slide-up.visible, .fade-in.visible { transform: translate(0); opacity: 1; }

@keyframes fadeUp {
  from { opacity: 0; transform: translateY(24px); }
  to   { opacity: 1; transform: none; }
}

@media (prefers-reduced-motion: reduce) {
  .slide-left, .slide-right, .fade-in, .slide-up { transition: none; }
  * { animation: none !important; }
}

@media (max-width: 900px) {
  nav { padding: 0 1.5rem; }
  .nav-links { gap: 1.2rem; }
  .hero-main { grid-template-columns: 1fr; padding: 2.5rem 1.5rem; gap: 2rem; }
  .challenge-index { grid-template-columns: repeat(2, 1fr); }
  .index-item:nth-child(2) { border-right: none; }
  .index-item:nth-child(3) { border-top: 1px solid var(--border); }
  .index-item:nth-child(4) { border-top: 1px solid var(--border); border-right: none; }
  .section-banner { padding: 1.8rem 1.5rem; gap: 1.5rem; }
  .banner-num { font-size: clamp(3.5rem, 15vw, 6rem); }
  .project-grid { grid-template-columns: 1fr; }
  .video-col,
  .project-section:nth-child(2) .video-col,
  .project-section:nth-child(4) .video-col { border: none; border-bottom: 1px solid var(--border); }
  .video-frame { padding: 1rem 1rem 0; }
  .text-col { padding: 2rem 1.5rem; }
}