/* bienphiendoan — shared site shell (topbar, layout, footer) */

:root {
  color-scheme: light dark;
  --bg: #ffffff;
  --fg: #111827;
  --muted: #6b7280;
  --border: #e5e7eb;
  --accent: #2563eb;
  --accent-fg: #ffffff;
  --surface: #fafafa;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0b0c10;
    --fg: #e5e7eb;
    --muted: #9ca3af;
    --border: #1f2937;
    --accent: #93c5fd;
    --accent-fg: #0b0c10;
    --surface: #11131a;
  }
}

* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; background: var(--bg); color: var(--fg); }
body {
  font-family: ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  line-height: 1.55;
  -webkit-font-smoothing: antialiased;
}
a { color: inherit; }

/* ---- top bar ---- */
header.topbar {
  position: sticky;
  top: 0;
  z-index: 10;
  background: color-mix(in srgb, var(--bg) 92%, transparent);
  backdrop-filter: saturate(160%) blur(8px);
  -webkit-backdrop-filter: saturate(160%) blur(8px);
  border-bottom: 1px solid var(--border);
}
.topbar-inner {
  max-width: 60rem;
  margin: 0 auto;
  padding: 0.85rem 1.25rem;
  display: flex;
  align-items: center;
  gap: 1.5rem;
}
.brand {
  font-weight: 700;
  letter-spacing: -0.01em;
  font-size: 1.05rem;
  text-decoration: none;
  color: var(--fg);
  white-space: nowrap;
}
.brand .dot { color: var(--accent); }
nav.primary { display: flex; gap: 1.25rem; flex: 1; }
nav.primary a {
  text-decoration: none;
  color: var(--muted);
  font-size: 0.94rem;
  padding: 0.3rem 0;
  border-bottom: 1px solid transparent;
  transition: color 120ms ease, border-color 120ms ease;
}
nav.primary a:hover,
nav.primary a:focus-visible,
nav.primary a[aria-current="page"] {
  color: var(--fg);
  border-bottom-color: var(--accent);
  outline: none;
}

.auth { display: flex; gap: 0.5rem; align-items: center; }

.btn {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.45rem 0.95rem;
  font-size: 0.9rem;
  font-weight: 500;
  border-radius: 6px;
  text-decoration: none;
  border: 1px solid var(--border);
  color: var(--fg);
  background: transparent;
  cursor: pointer;
  transition: background 120ms ease, border-color 120ms ease, color 120ms ease;
}
.btn:hover, .btn:focus-visible { background: var(--surface); outline: none; }
.btn.primary {
  background: var(--accent);
  border-color: var(--accent);
  color: var(--accent-fg);
}
.btn.primary:hover, .btn.primary:focus-visible {
  background: color-mix(in srgb, var(--accent) 88%, black);
  border-color: color-mix(in srgb, var(--accent) 88%, black);
}

@media (max-width: 560px) {
  .topbar-inner { flex-wrap: wrap; gap: 0.75rem 1rem; }
  nav.primary { order: 3; width: 100%; gap: 1rem; }
}

/* ---- content shell ---- */
main { max-width: 44rem; margin: 0 auto; padding: 4rem 1.25rem 6rem; }

.hero { margin: 0 0 4rem; }
.hero h1 {
  font-size: clamp(1.85rem, 4vw, 2.4rem);
  margin: 0 0 0.6rem;
  letter-spacing: -0.02em;
  line-height: 1.2;
}
.hero p { margin: 0; color: var(--muted); font-size: 1.05rem; max-width: 32rem; }

h2.section {
  font-size: 0.78rem;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--muted);
  margin: 0 0 1rem;
}

footer.site {
  margin-top: 5rem;
  padding-top: 1.25rem;
  border-top: 1px solid var(--border);
  color: var(--muted);
  font-size: 0.82rem;
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  flex-wrap: wrap;
}
footer.site a { color: var(--muted); }