.site-header {
  position: fixed;
  top: 0; left: 0; right: 0;
  z-index: 100;
  padding: 16px 0;
  transition: background var(--transition), box-shadow var(--transition);
}

.site-header.scrolled {
  background: var(--color-white);
  box-shadow: 0 2px 12px color-mix(in srgb, var(--color-main) 12%, transparent);
}

.nav-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.nav-logo {
  font-family: var(--font-heading);
  font-size: 1.3rem;
  font-weight: 700;
  color: var(--color-main-text);
  letter-spacing: 0.05em;
}
/* TOPページのヒーロー背景は明るい色のため、ヘッダーが透明な間も濃い文字色のままにする */
body.home .nav-logo,
body.home .nav-menu a { color: var(--color-text); }
body.home .site-header.scrolled .nav-logo,
body.home .site-header.scrolled .nav-menu a { color: var(--color-text); }

.nav-menu ul {
  display: flex;
  gap: 32px;
  list-style: none;
}

.nav-menu a {
  font-family: var(--font-heading);
  font-size: 0.85rem;
  letter-spacing: 0.08em;
  color: var(--color-text);
  position: relative;
}
.nav-menu a::after {
  content: '';
  position: absolute;
  bottom: -2px; left: 0; right: 0;
  height: 2px;
  background: var(--color-main);
  transform: scaleX(0);
  transition: transform var(--transition);
}
.nav-menu a:hover::after { transform: scaleX(1); opacity: 1; }

.nav-contact-btn {
  background: var(--color-footer-bg) !important;
  color: var(--color-white) !important;
  padding: 7px 20px;
  border: 2px solid var(--color-footer-bg);
  border-radius: 0;
  transition: background 0.3s ease, color 0.3s ease !important;
}
.nav-contact-btn:hover {
  background: var(--color-white) !important;
  color: var(--color-footer-bg) !important;
  opacity: 1 !important;
}
.nav-contact-btn::after { display: none !important; }

.hamburger {
  display: none;
  flex-direction: column;
  gap: 5px;
  background: none;
  border: none;
  cursor: pointer;
  padding: 4px;
}
.hamburger span {
  display: block;
  width: 24px;
  height: 2px;
  background: var(--color-main);
  border-radius: 2px;
  transition: all var(--transition);
}
.hamburger.open span:nth-child(1) { transform: translateY(7px) rotate(45deg); }
.hamburger.open span:nth-child(2) { opacity: 0; }
.hamburger.open span:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

/* ページ上部の余白（fixed ヘッダー分） */
body { padding-top: 64px; }
body.home { padding-top: 64px; }

@media (max-width: 768px) {
  .hamburger { display: flex; }

  .nav-menu {
    position: fixed;
    top: 0; left: 0; right: 0; bottom: 0;
    background: var(--color-white);
    display: flex;
    align-items: center;
    justify-content: center;
    opacity: 0;
    pointer-events: none;
    transition: opacity var(--transition);
    z-index: 101;
  }
  .nav-menu.open {
    opacity: 1;
    pointer-events: auto;
  }
  .nav-menu ul {
    flex-direction: column;
    align-items: center;
    gap: 24px;
  }
  .nav-menu a { font-size: 1.1rem; }
}