:root {
  --bg: #0f172a;
  --bg-alt: #111c32;
  --text: #e2e8f0;
  --muted: #94a3b8;
  --accent: #38bdf8;
  --accent-strong: #0ea5e9;
  --border: rgba(148, 163, 184, 0.25);
  color-scheme: dark;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: "Inter", "Segoe UI", Helvetica, Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
}

a {
  color: var(--accent);
  text-decoration: none;
  transition: color 0.2s ease;
}

a:hover,
a:focus {
  color: var(--accent-strong);
}

.container {
  width: min(1100px, 92vw);
  margin: 0 auto;
  padding: 0 1rem;
}

.site-header {
  backdrop-filter: blur(8px);
  background: rgba(15, 23, 42, 0.85);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 10;
}

.site-header .container {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 1rem 1.5rem;
}

.site-header .brand {
  font-weight: 600;
  letter-spacing: 0.02em;
}

.site-header nav a {
  font-size: 0.95rem;
  font-weight: 500;
}

.site-footer {
  border-top: 1px solid var(--border);
  margin-top: 3rem;
  background: rgba(15, 23, 42, 0.75);
}

.site-footer .container {
  padding: 2rem 1.5rem;
  font-size: 0.9rem;
  color: var(--muted);
}

main {
  display: block;
}

.hero {
  padding: 5.5rem 0 3rem;
  text-align: center;
}

.hero h1 {
  font-size: clamp(2.5rem, 5vw, 3.5rem);
  margin-bottom: 1rem;
  letter-spacing: 0.01em;
}

.hero p {
  color: var(--muted);
  font-size: 1.1rem;
  max-width: 620px;
  margin: 0 auto 2rem;
}

.hero .author-credit {
  color: var(--muted);
  font-size: 1rem;
  margin: -0.6rem auto 2.2rem;
}

.hero .status-note {
  color: var(--accent);
  font-size: 0.98rem;
  margin: -1.2rem auto 2.4rem;
}

.hero .cta {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  padding: 0.75rem 1.5rem;
  border-radius: 999px;
  background: linear-gradient(135deg, var(--accent), var(--accent-strong));
  color: #0f172a;
  font-weight: 600;
  box-shadow: 0 12px 30px rgba(56, 189, 248, 0.3);
}

.hero .cta:hover {
  transform: translateY(-1px);
  box-shadow: 0 16px 40px rgba(14, 165, 233, 0.35);
}

.section-title {
  font-size: 1.6rem;
  margin: 0 0 1.5rem;
  letter-spacing: 0.02em;
}

.lecture-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 1.5rem;
  padding: 0 0 3.5rem;
}

.lecture-card {
  background: var(--bg-alt);
  padding: 1.6rem;
  border-radius: 18px;
  border: 1px solid rgba(56, 189, 248, 0.08);
  box-shadow: 0 15px 35px rgba(15, 23, 42, 0.45);
  transition: transform 0.25s ease, box-shadow 0.25s ease;
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.lecture-card:hover {
  transform: translateY(-6px);
  box-shadow: 0 25px 45px rgba(14, 165, 233, 0.18);
}

.lecture-card .lecture-number {
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--accent);
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.lecture-card h3 {
  margin: 0;
  font-size: 1.25rem;
  line-height: 1.4;
}

.lecture-card p {
  margin: 0;
  color: var(--muted);
  font-size: 0.95rem;
}

.lecture-card .actions {
  margin-top: auto;
  display: flex;
  gap: 0.75rem;
  align-items: center;
}

.lecture-card .actions a {
  font-weight: 600;
}

.highlight {
  background: rgba(56, 189, 248, 0.08);
  border: 1px solid rgba(56, 189, 248, 0.2);
  border-radius: 14px;
  padding: 1.8rem;
  margin-bottom: 3rem;
}

.highlight h2 {
  margin: 0 0 1rem;
  font-size: 1.4rem;
}

.highlight ul {
  margin: 0;
  padding-left: 1.1rem;
  color: var(--muted);
}

.highlight li {
  margin-bottom: 0.5rem;
}

.lecture-page main {
  width: min(960px, 92vw);
  margin: 0 auto;
  padding-top: 4.5rem;
}

.lecture-page .jp-Notebook {
  border-radius: 18px;
  overflow: hidden;
  border: 1px solid rgba(148, 163, 184, 0.18);
  box-shadow: 0 20px 55px rgba(15, 23, 42, 0.5);
  margin-bottom: 3rem;
}

.lecture-page .jp-Notebook .jp-Cell {
  border-bottom: 1px solid rgba(148, 163, 184, 0.07);
}

@media (max-width: 680px) {
  .site-header .container {
    flex-direction: column;
    gap: 0.5rem;
  }
  .hero {
    padding-top: 4rem;
  }
  .lecture-card {
    padding: 1.4rem;
  }
}