/* =============================================
   header.css — sticky header, nav, mobile menu
   ============================================= */

.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background: rgba(251, 251, 253, .92);
  backdrop-filter: saturate(180%) blur(10px);
  -webkit-backdrop-filter: saturate(180%) blur(10px);
  border-bottom: 1px solid var(--border);
}

.header-inner {
  height: var(--header-height);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
}

.brand {
  font-family: var(--font-serif);
  font-weight: 700;
  font-size: 1.25rem;
  color: var(--text);
  letter-spacing: -0.01em;
  white-space: nowrap;
}
.brand:hover { text-decoration: none; color: var(--accent-dark); }

/* Nav — mobile-first: hidden dropdown panel */
.main-nav {
  position: fixed;
  inset: var(--header-height) 0 auto 0;
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  box-shadow: var(--shadow-md);
  padding: 1rem 1.25rem 1.5rem;
  transform: translateY(-115%);
  visibility: hidden;
  transition: transform .25s ease, visibility .25s ease;
}

.main-nav ul {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: .2rem;
}

.main-nav a {
  display: block;
  padding: .7rem .25rem;
  font-size: 1.05rem;
  font-weight: 500;
  color: var(--text-muted);
}
.main-nav a:hover { color: var(--text); text-decoration: none; }

body.nav-open .main-nav {
  transform: translateY(0);
  visibility: visible;
}

body.nav-open { overflow: hidden; }

.header-actions {
  display: flex;
  align-items: center;
  gap: .9rem;
}

/* Burger */
.nav-toggle {
  display: inline-flex;
  flex-direction: column;
  justify-content: center;
  gap: 5px;
  width: 42px;
  height: 42px;
  padding: 9px;
  background: transparent;
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-sm);
  cursor: pointer;
}
.nav-toggle span {
  display: block;
  height: 2px;
  width: 100%;
  background: var(--text);
  border-radius: 2px;
  transition: transform .2s ease, opacity .2s ease;
}

body.nav-open .nav-toggle span:nth-child(1) { transform: translateY(7px) rotate(45deg); }
body.nav-open .nav-toggle span:nth-child(2) { opacity: 0; }
body.nav-open .nav-toggle span:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

/* Desktop */
@media (min-width: 900px) {
  .main-nav {
    position: static;
    transform: none;
    visibility: visible;
    background: transparent;
    box-shadow: none;
    border: 0;
    padding: 0;
  }
  .main-nav ul { flex-direction: row; align-items: center; gap: 1.75rem; }
  .main-nav a { display: inline; padding: 0; font-size: .95rem; }
  .nav-toggle { display: none; }
}