/* Sticky Header & Navigation */
header.nav {
  position: sticky;
  top: 0;
  z-index: 50;
  background: var(--nav-bg);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--nav-border);
  transition: background-color 0.25s, border-color 0.25s;
}

.nav-in {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 72px;
}

.brand {
  display: flex;
  align-items: center;
  gap: 12px;
  font-family: "Fraunces", Georgia, serif;
  font-weight: 700;
  font-size: 19px;
  color: var(--text-heading);
  text-decoration: none;
  line-height: 1.15;
}

.brand .mark {
  width: 38px;
  height: 38px;
  flex: none;
  object-fit: contain;
}

.nav-links {
  display: flex;
  gap: 28px;
  align-items: center;
}

.nav-links a {
  font-size: 15px;
  font-weight: 500;
  color: var(--text-muted);
  transition: color 0.18s ease;
}

.nav-links a:hover {
  color: var(--blue-lt);
}

.nav-actions {
  display: flex;
  align-items: center;
  gap: 12px;
}

/* Dark Mode Toggle Button */
.theme-toggle {
  background: var(--sky);
  border: 1px solid var(--border);
  color: var(--text-main);
  cursor: pointer;
  padding: 8px 12px;
  border-radius: 999px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  font-size: 13px;
  font-weight: 600;
  transition: background-color 0.2s, border-color 0.2s, transform 0.15s;
}

.theme-toggle:hover {
  background: var(--border);
  transform: scale(1.04);
}

.theme-toggle svg {
  width: 17px;
  height: 17px;
  flex: none;
}

.theme-toggle .icon-sun {
  display: none;
}

.theme-toggle .icon-moon {
  display: block;
}

[data-theme="dark"] .theme-toggle .icon-sun {
  display: block;
}

[data-theme="dark"] .theme-toggle .icon-moon {
  display: none;
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) .theme-toggle .icon-sun {
    display: block;
  }
  :root:not([data-theme="light"]) .theme-toggle .icon-moon {
    display: none;
  }
}

/* Mobile Hamburger Button */
.burger {
  display: none;
  background: none;
  border: 0;
  cursor: pointer;
  padding: 8px;
  position: relative;
  z-index: 60;
}

.burger span {
  display: block;
  width: 24px;
  height: 2px;
  background: var(--text-main);
  margin: 5px 0;
  transition: transform 0.22s ease, opacity 0.22s ease, background-color 0.22s ease;
  border-radius: 2px;
}

/* Hamburger Active / Open State (Morph to X) */
.burger[aria-expanded="true"] span:nth-child(1) {
  transform: translateY(7px) rotate(45deg);
}

.burger[aria-expanded="true"] span:nth-child(2) {
  opacity: 0;
}

.burger[aria-expanded="true"] span:nth-child(3) {
  transform: translateY(-7px) rotate(-45deg);
}

/* Mobile Nav Drawer */
@media (max-width: 900px) {
  .burger {
    display: block;
  }

  .nav-links {
    position: fixed;
    inset: 72px 0 auto 0;
    background: var(--bg-page);
    flex-direction: column;
    gap: 0;
    padding: 12px 0 20px;
    border-bottom: 1px solid var(--border);
    box-shadow: var(--shadow-lg);
    transform: translateY(-150%);
    transition: transform 0.28s cubic-bezier(0.4, 0, 0.2, 1);
    z-index: 40;
  }

  .nav-links.open {
    transform: translateY(0);
  }

  .nav-links a {
    padding: 14px 24px;
    width: 100%;
    border-bottom: 1px solid var(--border-subtle);
    font-size: 16px;
  }

  .nav-links a:last-child {
    border-bottom: none;
  }
}