:root {
  --bg: #0f1419;
  --bg-alt: #1a2332;
  --surface: #243044;
  --text: #e8eef7;
  --muted: #9fb0c8;
  --accent: #3dd68c;
  --accent-dim: #2a9d63;
  --border: #334155;
  --radius: 12px;
  --font: system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  --mono: ui-monospace, "Cascadia Code", "Fira Code", monospace;
}

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

body {
  margin: 0;
  font-family: var(--font);
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
}

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

a:hover {
  text-decoration: underline;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 10;
  background: rgba(15, 20, 25, 0.92);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--border);
}

.nav {
  max-width: 1100px;
  margin: 0 auto;
  padding: 1rem 1.25rem;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 1rem 1.5rem;
}

.logo {
  font-weight: 700;
  color: var(--text);
  margin-right: auto;
}

.logo:hover {
  color: var(--accent);
  text-decoration: none;
}

main {
  max-width: 1100px;
  margin: 0 auto;
  padding: 0 1.25rem 3rem;
}

.hero {
  padding: 3rem 0 2.5rem;
}

.eyebrow {
  color: var(--accent);
  font-size: 0.875rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  margin: 0 0 0.5rem;
}

.hero h1 {
  font-size: clamp(1.75rem, 4vw, 2.75rem);
  line-height: 1.2;
  margin: 0 0 1rem;
}

.lead {
  color: var(--muted);
  font-size: 1.1rem;
  max-width: 42rem;
  margin: 0 0 1.5rem;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
}

.btn {
  display: inline-block;
  padding: 0.65rem 1.25rem;
  border-radius: 8px;
  font-weight: 600;
  border: none;
  cursor: pointer;
  font-size: 0.95rem;
  text-decoration: none;
}

.btn-primary {
  background: var(--accent);
  color: #0a1610;
}

.btn-primary:hover {
  background: var(--accent-dim);
  text-decoration: none;
}

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

.btn-secondary:hover {
  border-color: var(--accent);
  text-decoration: none;
}

.section {
  padding: 2.5rem 0;
}

.section-alt {
  background: var(--bg-alt);
  margin: 0 -1.25rem;
  padding: 2.5rem 1.25rem;
  border-radius: var(--radius);
}

.section h2 {
  margin: 0 0 0.5rem;
  font-size: 1.5rem;
}

.section-note {
  color: var(--muted);
  margin: 0 0 1.5rem;
}

.section-note code {
  font-family: var(--mono);
  font-size: 0.9em;
  background: var(--surface);
  padding: 0.15em 0.4em;
  border-radius: 4px;
}

.grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 1rem;
}

.project-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.project-card h3 {
  margin: 0;
  font-size: 1.05rem;
}

.project-card p {
  margin: 0;
  color: var(--muted);
  font-size: 0.9rem;
  flex: 1;
}

.project-card .tag {
  font-size: 0.75rem;
  color: var(--accent);
  font-weight: 600;
}

.project-card a.card-link {
  font-size: 0.875rem;
  font-weight: 600;
}

.demo-card {
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem;
  margin-bottom: 1.25rem;
}

.demo-card h3 {
  margin: 0 0 1rem;
}

.demo-body {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.btn-row {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.btn-row button {
  padding: 0.5rem 1rem;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text);
  cursor: pointer;
  font-weight: 600;
}

.btn-row button:hover {
  border-color: var(--accent);
  color: var(--accent);
}

.demo-result,
.demo-status {
  margin: 0;
  color: var(--muted);
  min-height: 1.5em;
}

.demo-form {
  display: grid;
  gap: 0.75rem;
  max-width: 320px;
}

.demo-form label {
  display: flex;
  flex-direction: column;
  gap: 0.25rem;
  font-size: 0.875rem;
  color: var(--muted);
}

.demo-form input {
  padding: 0.5rem 0.65rem;
  border-radius: 6px;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text);
  font-size: 1rem;
}

.inline-form {
  grid-template-columns: 1fr 1fr auto;
  max-width: 100%;
  align-items: end;
}

@media (max-width: 600px) {
  .inline-form {
    grid-template-columns: 1fr;
  }
}

.ttt-board {
  display: grid;
  grid-template-columns: repeat(3, 4rem);
  gap: 4px;
  width: fit-content;
}

.ttt-board button {
  width: 4rem;
  height: 4rem;
  font-size: 1.5rem;
  font-weight: 700;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--surface);
  color: var(--text);
  cursor: pointer;
}

.ttt-board button:disabled {
  cursor: default;
}

.ttt-board button.win {
  background: rgba(61, 214, 140, 0.25);
  border-color: var(--accent);
}

.grade-list {
  list-style: none;
  padding: 0;
  margin: 0.75rem 0 0;
}

.grade-list li {
  display: flex;
  justify-content: space-between;
  padding: 0.5rem 0;
  border-bottom: 1px solid var(--border);
  font-size: 0.95rem;
}

.grade-list .letter {
  font-weight: 700;
  color: var(--accent);
}

.site-footer {
  text-align: center;
  padding: 2rem 1.25rem;
  color: var(--muted);
  font-size: 0.875rem;
  border-top: 1px solid var(--border);
}

.site-footer p {
  margin: 0;
}