/* ============================================================
   NAV — Fixed header · Desktop links · Mobile slide panel
   ============================================================ */

.site-header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 100;
  background: rgba(246, 248, 252, 0.82);
  backdrop-filter: blur(18px);
  -webkit-backdrop-filter: blur(18px);
  border-bottom: 1px solid rgba(220, 227, 239, 0.6);
  transition: border-color 0.2s ease, box-shadow 0.2s ease;
}

.site-header.scrolled {
  border-bottom-color: var(--divider);
  box-shadow: 0 8px 28px rgba(15, 23, 42, 0.08);
}

.nav-shell {
  height: 72px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--sp-md);
}

/* ── Brand ── */
.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  text-decoration: none;
  flex-shrink: 0;
}

.brand-mark {
  width: 32px;
  height: 32px;
  background: var(--ink);
  border-radius: 6px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--font-mono);
  font-size: 13px;
  font-weight: 500;
  color: var(--bg);
  letter-spacing: -0.5px;
  flex-shrink: 0;
}

.brand-word {
  font-family: var(--font-display);
  font-size: 16px;
  font-weight: 700;
  color: var(--ink);
  letter-spacing: -0.02em;
  white-space: nowrap;
}

.mobile-controls {
  display: none;
  align-items: center;
  gap: 10px;
}

/* ── Desktop nav ── */
.desktop-nav {
  display: flex;
  align-items: center;
  gap: 28px;
}

.nav-link {
  font-family: var(--font-body);
  font-size: 12px;
  font-weight: 400;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--body-text);
  text-decoration: none;
  transition: color 0.15s ease;
  position: relative;
}

.nav-link::after {
  content: "";
  position: absolute;
  left: 0;
  bottom: -8px;
  width: 100%;
  height: 2px;
  background: var(--primary);
  transform: scaleX(0);
  transform-origin: left;
  transition: transform 0.2s ease;
}

.nav-link:hover,
.nav-link.is-active {
  color: var(--ink);
  text-decoration: none;
}
.nav-link:hover::after,
.nav-link.is-active::after { transform: scaleX(1); }

/* ── Nav CTA ── */
.nav-cta {
  font-size: 12px;
  font-weight: 600;
  padding: 11px 16px;
  border-radius: 999px;
}

/* ── Hamburger ── */
.menu-toggle {
  display: none;
  flex-direction: column;
  justify-content: center;
  gap: 5px;
  width: 40px;
  height: 40px;
  padding: 8px;
  background: transparent;
  border: none;
  cursor: pointer;
  border-radius: 4px;
}

.menu-toggle span {
  display: block;
  width: 20px;
  height: 2px;
  background: var(--ink);
  border-radius: 2px;
  transition: transform 0.25s ease, opacity 0.25s ease;
  transform-origin: center;
}

.menu-toggle[aria-expanded="true"] span:nth-child(1) {
  transform: translateY(7px) rotate(45deg);
}
.menu-toggle[aria-expanded="true"] span:nth-child(2) {
  opacity: 0;
}
.menu-toggle[aria-expanded="true"] span:nth-child(3) {
  transform: translateY(-7px) rotate(-45deg);
}

/* ── Mobile nav panel ── */
.mobile-nav {
  position: fixed;
  top: 0;
  right: 0;
  bottom: 0;
  width: min(390px, 100vw);
  background: var(--surface);
  z-index: 99;
  padding: 80px var(--sp-lg) var(--sp-lg);
  display: flex;
  flex-direction: column;
  gap: var(--sp-md);
  transform: translateX(100%);
  transition: transform 0.3s ease;
  box-shadow: -20px 0 44px rgba(15,23,42,0.18);
}

.mobile-nav.is-open {
  transform: translateX(0);
}

.mobile-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(15,23,42,0.3);
  z-index: 98;
  backdrop-filter: blur(2px);
}
.mobile-overlay.is-open { display: block; }

.mobile-link {
  display: block;
  font-size: 30px;
  font-family: var(--font-display);
  font-weight: 700;
  color: var(--ink);
  letter-spacing: -0.03em;
  text-decoration: none;
  line-height: 1;
  transition: color 0.15s ease;
}
.mobile-link:hover { color: var(--primary); text-decoration: none; }

.mobile-cta {
  margin-top: auto;
  align-self: flex-start;
}

/* ── Dark mode toggle ── */
.theme-toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  border-radius: 50%;
  border: 1px solid var(--divider);
  background: var(--surface);
  cursor: pointer;
  color: var(--ink);
  transition: background 0.2s ease, border-color 0.2s ease, transform 0.15s ease;
  flex-shrink: 0;
}

.theme-toggle:hover {
  background: var(--primary-soft);
  border-color: var(--primary);
  transform: scale(1.05);
}

.theme-toggle svg {
  width: 16px;
  height: 16px;
  transition: transform 0.4s ease, opacity 0.3s ease;
  position: absolute;
}

.theme-toggle { position: relative; }

.icon-sun  { opacity: 1; }
.icon-moon { opacity: 0; transform: rotate(-90deg); }

html[data-theme="dark"] .icon-sun  { opacity: 0; transform: rotate(90deg); }
html[data-theme="dark"] .icon-moon { opacity: 1; transform: rotate(0deg); }

/* ── Responsive ── */
@media (max-width: 900px) {
  .desktop-nav { display: none; }
  .menu-toggle { display: flex; }
  .mobile-controls { display: flex; }
}