.site-header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 100;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 1rem clamp(1rem, 4vw, 3rem);
  transition: background .25s ease, box-shadow .25s ease, transform .25s ease;
}
.site-header.scrolled,
.site-header.solid {
  background: rgba(255, 248, 238, .9);
  background: color-mix(in srgb, var(--paper) 88%, transparent);
  backdrop-filter: blur(14px);
  box-shadow: 0 12px 30px rgba(0,0,0,.08);
}

html[data-theme="night"] .site-header.scrolled,
html[data-theme="night"] .site-header.solid {
  background: rgba(35, 35, 41, .92);
  background: color-mix(in srgb, var(--paper) 90%, transparent);
}

.brand {
  display: flex;
  align-items: center;
  gap: .75rem;
  text-decoration: none;
  font-weight: 900;
  position: relative;
  z-index: 104;
}
.brand-mark {
  display: inline-grid;
  place-items: center;
  width: 3.1rem;
  height: 3.1rem;
  border: 3px solid var(--ink);
  border-radius: 1rem;
  background: var(--paper);
  box-shadow: 4px 4px 0 rgba(0,0,0,.15);
  letter-spacing: -.1em;
}
.brand-text { font-size: .95rem; }
.primary-nav {
  display: flex;
  align-items: center;
  gap: clamp(.65rem, 2vw, 1.3rem);
  font-size: .9rem;
  font-weight: 900;
}
.primary-nav a {
  text-decoration: none;
  padding: .5rem .1rem;
  position: relative;
}
.primary-nav a::after {
  content: "";
  position: absolute;
  left: 0;
  bottom: .25rem;
  width: 100%;
  height: .45rem;
  background: var(--sun);
  z-index: -1;
  transform: scaleX(0);
  transform-origin: left;
  transition: transform .25s ease;
  border-radius: 999px;
}
.primary-nav a:hover::after, .primary-nav a.active::after { transform: scaleX(1); }
.theme-toggle {
  width: 4.1rem;
  height: 2rem;
  border: 3px solid currentColor;
  background: var(--paper-soft);
  border-radius: 999px;
  padding: .15rem;
  cursor: pointer;
  box-shadow: 3px 3px 0 rgba(0,0,0,.12);
}
.toggle-dot {
  display: block;
  width: 1.25rem;
  height: 1.25rem;
  border-radius: 50%;
  background: var(--sun);
  transition: transform .25s cubic-bezier(.34,1.56,.64,1), background .25s ease;
}
html[data-theme="night"] .toggle-dot { transform: translateX(2rem); background: var(--lavender); }
.menu-toggle {
  display: none;
  position: relative;
  z-index: 104;
  width: 3rem;
  height: 3rem;
  border: 3px solid var(--ink);
  border-radius: .9rem;
  background: var(--paper);
  padding: .55rem;
  cursor: pointer;
}
.menu-toggle span {
  display: block;
  height: 3px;
  width: 100%;
  background: var(--ink);
  border-radius: 99px;
  margin: .27rem 0;
  transition: transform .25s ease, opacity .2s ease;
}
.menu-toggle.open span:nth-child(1) { transform: translateY(8px) rotate(45deg); }
.menu-toggle.open span:nth-child(2) { opacity: 0; }
.menu-toggle.open span:nth-child(3) { transform: translateY(-8px) rotate(-45deg); }