:root {
  --bg: #f7f9fc;
  --card: #ffffff;
  --ink: #0e1a2b;
  --muted: #4a5b74;
  --line: #d7dfea;
  --accent: #0f766e;
  --accent-hover: #0a5f59;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
  color: var(--ink);
  background: linear-gradient(180deg, #eef4fb 0%, var(--bg) 30%);
  line-height: 1.55;
}

.hero,
main,
footer {
  width: min(1024px, 92vw);
  margin: 0 auto;
}

.hero {
  padding: 2.5rem 0 1.2rem;
}

.eyebrow {
  margin: 0;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--muted);
  font-size: 0.78rem;
}

h1 {
  margin: 0.4rem 0;
  font-size: clamp(1.6rem, 2.5vw, 2.4rem);
  line-height: 1.2;
}

.subtitle {
  margin: 0.4rem 0 1.1rem;
  color: var(--muted);
  max-width: 62ch;
}

.paper-link {
  display: inline-block;
  text-decoration: none;
  background: var(--accent);
  color: #fff;
  padding: 0.55rem 0.9rem;
  border-radius: 0.5rem;
  font-weight: 600;
}

.paper-link:hover,
.paper-link:focus-visible {
  background: var(--accent-hover);
}

.intro {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 0.75rem;
  padding: 1rem 1.1rem;
}

.group {
  margin-top: 1.4rem;
}

.group h2 {
  margin: 0 0 0.7rem;
  font-size: 1.15rem;
}

.video-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  gap: 0.85rem;
}

.video-card {
  border: 1px solid var(--line);
  background: var(--card);
  border-radius: 0.75rem;
  overflow: hidden;
}

.video-button {
  display: block;
  width: 100%;
  border: 0;
  padding: 0;
  margin: 0;
  background: transparent;
  cursor: pointer;
  text-align: left;
}

.video-thumb {
  width: 100%;
  display: block;
  aspect-ratio: 16 / 9;
  object-fit: cover;
}

.video-meta {
  padding: 0.65rem 0.75rem 0.8rem;
}

.video-title {
  margin: 0;
  font-size: 0.96rem;
  line-height: 1.35;
}

.video-note {
  margin: 0.45rem 0 0;
  font-size: 0.82rem;
  color: var(--muted);
}

.video-frame {
  width: 100%;
  aspect-ratio: 16 / 9;
  border: 0;
  display: block;
}

footer {
  padding: 1.7rem 0 2.1rem;
  color: var(--muted);
}