:root {
  --bg: #0d1117;
  --bg2: #161b22;
  --border: #30363d;
  --accent: #58a6ff;
  --accent2: #3fb950;
  --text: #e6edf3;
  --muted: #8b949e;
}

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

html { scroll-behavior: smooth; }

body {
  background: var(--bg);
  color: var(--text);
  font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
  line-height: 1.6;
}

/* ── Nav ── */
nav {
  position: fixed;
  top: 0; left: 0; right: 0;
  z-index: 100;
  backdrop-filter: blur(12px);
  background: rgba(13,17,23,0.85);
  border-bottom: 1px solid var(--border);
  padding: 0 2rem;
  height: 56px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.nav-logo {
  font-family: 'Courier New', monospace;
  font-size: 1rem;
  color: var(--accent2);
  font-weight: 700;
  letter-spacing: 0.05em;
}

.nav-logo span { color: var(--muted); }

nav ul {
  list-style: none;
  display: flex;
  gap: 2rem;
}

nav a {
  color: var(--muted);
  text-decoration: none;
  font-size: 0.875rem;
  transition: color 0.2s;
}

nav a:hover { color: var(--text); }

/* ── Hero ── */

.hero {
  min-height: 40vh;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 4rem 2rem 2rem;
  position: relative;
  overflow: hidden;
}

.hero::before {
  content: '';
  position: absolute;
  inset: 0;
  background:
    radial-gradient(ellipse 60% 50% at 50% 0%, rgba(88,166,255,0.08) 0%, transparent 70%),
    radial-gradient(ellipse 40% 40% at 80% 80%, rgba(63,185,80,0.06) 0%, transparent 60%);
  pointer-events: none;
}

.hero-inner {
  max-width: 700px;
  width: 100%;
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  background: rgba(63,185,80,0.1);
  border: 1px solid rgba(63,185,80,0.3);
  border-radius: 100px;
  padding: 0.25rem 0.75rem;
  font-size: 0.75rem;
  color: var(--accent2);
  margin-bottom: 1.5rem;
  font-family: 'Courier New', monospace;
}

.dot {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--accent2);
  animation: pulse 2s ease-in-out infinite;
}

@keyframes pulse {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.3; }
}

.hero h1 {
  font-size: clamp(2rem, 5.5vw, 3.5rem);
  font-weight: 700;
  line-height: 1.1;
  letter-spacing: -0.02em;
  margin-bottom: 1rem;
}

.hero h1 .highlight {
  background: linear-gradient(135deg, var(--accent), var(--accent2));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero p {
  color: var(--muted);
  font-size: 1.125rem;
  max-width: 480px;
  margin-bottom: 1.5rem;
}

.hero-actions {
  display: flex;
  gap: 1rem;
  flex-wrap: wrap;
}

.btn {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.625rem 1.25rem;
  border-radius: 6px;
  font-size: 0.875rem;
  font-weight: 500;
  text-decoration: none;
  transition: all 0.2s;
  cursor: pointer;
  border: none;
}

.btn-primary {
  background: var(--accent);
  color: #0d1117;
}

.btn-primary:hover {
  background: #79c0ff;
  transform: translateY(-1px);
}

.btn-ghost {
  background: transparent;
  color: var(--text);
  border: 1px solid var(--border);
}

.btn-ghost:hover {
  border-color: var(--muted);
  background: var(--bg2);
}

/* ── OEIS Section ── */
.oeis-section {
  padding: 2rem 2rem;
  max-width: 700px;
  margin: 0 auto;
}

.section-label {
  font-family: 'Courier New', monospace;
  font-size: 1rem;
  color: var(--accent);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-bottom: 0.5rem;
}

.oeis-section h2 {
  font-size: 1.5rem;
  font-weight: 700;
  margin-bottom: 1.5rem;
}

.oeis-card {
  background: var(--bg2);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 1.25rem 1.5rem;
}

.oeis-meta {
  display: flex;
  gap: 1.5rem;
  margin-bottom: 1rem;
  font-size: 0.875rem;
  color: var(--muted);
  font-family: 'Courier New', monospace;
}

.oeis-meta span { color: var(--text); }

.oeis-numbers {
  font-family: 'Courier New', monospace;
  font-size: 1rem;
  color: var(--muted);
  line-height: 1.8;
  word-break: break-all;
}

.oeis-num {
  display: inline-block;
  animation: wave-highlight 16s linear infinite;
}

@keyframes wave-highlight {
  0%, 44%, 56%, 100% { color: var(--muted); text-shadow: none; }
  50% { color: var(--accent2); text-shadow: 0 0 8px rgba(63,185,80,0.7); }
}

.oeis-loading {
  color: var(--muted);
  font-size: 0.875rem;
  font-family: 'Courier New', monospace;
}

.oeis-desc {
  font-size: 0.95rem;
  color: var(--muted);
  margin-bottom: 1.25rem;
}

.sloanesnote {
  margin-top: 1rem;
  font-size: 0.8rem;
  color: var(--muted);
  line-height: 1.6;
}

.sloanesnote code {
  font-family: 'Courier New', monospace;
  color: var(--accent2);
}

.sloanesnote a,
.oeis-desc a { color: #79c0ff; text-decoration: underline; }
.sloanesnote a:hover { text-decoration: underline; }

/* ── Footer ── */
footer {
  border-top: 1px solid var(--border);
  padding: 1rem 2rem;
  text-align: center;
  color: var(--muted);
  font-size: 0.8rem;
  font-family: 'Courier New', monospace;
}

footer a {
  color: var(--accent);
  text-decoration: none;
}

footer a:hover { text-decoration: underline; }

/* ── Responsive ── */
@media (max-width: 600px) {
  nav ul { gap: 1.2rem; }
}