:root {
  --bg: #f8fafc;
  --surface: #ffffff;
  --text: #0f172a;
  --muted: #475569;
  --border: #e2e8f0;
  --accent: #2563eb;
  --accent-soft: #dbeafe;
  --shadow: 0 8px 24px rgba(15, 23, 42, 0.08);
}

:root[data-theme='dark'] {
  --bg: #020617;
  --surface: #0f172a;
  --text: #f8fafc;
  --muted: #cbd5e1;
  --border: #1e293b;
  --accent: #60a5fa;
  --accent-soft: rgba(96, 165, 250, 0.18);
  --shadow: 0 10px 30px rgba(2, 6, 23, 0.45);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: Inter, system-ui, -apple-system, Segoe UI, Roboto, sans-serif;
  line-height: 1.65;
}

a { color: var(--accent); }

.container { width: min(1080px, 92vw); margin: 0 auto; }

.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  border-bottom: 1px solid var(--border);
  background: color-mix(in srgb, var(--bg) 88%, transparent);
  backdrop-filter: blur(8px);
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 0.85rem 0;
}

.logo {
  text-decoration: none;
  color: var(--text);
  font-weight: 800;
  letter-spacing: 0.02em;
}

.nav-links { display: flex; flex-wrap: wrap; gap: 0.85rem; }
.nav-links a {
  color: var(--muted);
  text-decoration: none;
  font-weight: 600;
  border-bottom: 2px solid transparent;
}
.nav-links a.active,
.nav-links a:hover {
  color: var(--text);
  border-color: var(--accent);
}

.theme-toggle {
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text);
  border-radius: 999px;
  padding: 0.45rem 0.75rem;
  cursor: pointer;
}

main { padding: 1rem 0 2rem; }

.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 16px;
  box-shadow: var(--shadow);
  padding: 1.25rem;
  margin: 0 0 1rem;
  opacity: 0;
  transform: translateY(8px);
  transition: 0.45s ease;
}
.card.visible { opacity: 1; transform: translateY(0); }

h1, h2, h3 { line-height: 1.2; margin-top: 0; }
h1 { font-size: clamp(2rem, 6vw, 3rem); margin-bottom: 0.4rem; }
h2 { font-size: clamp(1.35rem, 3vw, 1.95rem); margin-bottom: 0.8rem; }
.subtitle { color: var(--muted); font-size: 1.1rem; margin: 0 0 1rem; }

.eyebrow {
  margin: 0 0 0.4rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--accent);
  font-weight: 700;
  font-size: 0.8rem;
}

.btn-row { display: flex; flex-wrap: wrap; gap: 0.6rem; }
.btn {
  display: inline-block;
  padding: 0.65rem 0.95rem;
  border-radius: 10px;
  text-decoration: none;
  font-weight: 700;
  border: 1px solid var(--border);
}
.btn.primary { background: var(--accent); color: #fff; border-color: var(--accent); }
.btn.ghost { color: var(--text); }

.chips { list-style: none; padding: 0; margin: 0; display: flex; flex-wrap: wrap; gap: 0.45rem; }
.chips li {
  background: var(--accent-soft);
  border: 1px solid color-mix(in srgb, var(--accent) 25%, var(--border));
  border-radius: 999px;
  padding: 0.3rem 0.65rem;
  font-size: 0.88rem;
  font-weight: 600;
}

.grid-2 { display: grid; gap: 1rem; }
.timeline { border-left: 2px solid var(--accent-soft); padding-left: 0.9rem; }
.timeline-item + .timeline-item { margin-top: 0.8rem; }
.role-meta { color: var(--muted); font-size: 0.92rem; }

.diagram-box {
  border: 1px dashed var(--border);
  border-radius: 12px;
  padding: 0.8rem;
  background: color-mix(in srgb, var(--surface) 90%, var(--accent-soft));
}

.todo {
  border-left: 3px solid #f59e0b;
  background: #fef3c7;
  color: #78350f;
  padding: 0.65rem;
  border-radius: 8px;
}
:root[data-theme='dark'] .todo {
  background: rgba(245, 158, 11, 0.18);
  color: #fde68a;
}

footer {
  border-top: 1px solid var(--border);
  color: var(--muted);
  text-align: center;
  padding: 1rem 0 2rem;
  font-size: 0.9rem;
}

form { display: grid; gap: 0.7rem; }
input, textarea {
  width: 100%;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text);
  border-radius: 10px;
  padding: 0.65rem 0.75rem;
  font: inherit;
}

@media (min-width: 780px) {
  .grid-2 { grid-template-columns: 1fr 1fr; }
  .card { padding: 1.5rem; }
}