/* ============================================================
   STUDIO Butter — Header & Navigation
   ============================================================ */

.site-header {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  z-index: 1000;
  padding: var(--space-md) 0;
  transition:
    background-color var(--duration-normal) var(--ease-out),
    backdrop-filter var(--duration-normal) var(--ease-out),
    padding var(--duration-normal) var(--ease-out);
}

/* Scrolled state: glass morphism */
.site-header.is-scrolled,
.site-header.always-scrolled {
  background-color: rgba(255, 255, 255, 0.9);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  padding: var(--space-sm) 0;
  border-bottom: 1px solid var(--color-border-subtle);
}

.site-header.is-scrolled .site-logo__sub,
.site-header.always-scrolled .site-logo__sub {
  color: var(--color-text-secondary);
}

.site-header.is-scrolled .site-logo__main,
.site-header.always-scrolled .site-logo__main {
  color: var(--color-text-secondary);
}

.site-header.is-scrolled .site-logo:hover .site-logo__main,
.site-header.always-scrolled .site-logo:hover .site-logo__main {
  color: var(--color-accent);
}

.site-header.is-scrolled .nav-desktop__link,
.site-header.always-scrolled .nav-desktop__link {
  color: var(--color-text-secondary);
}

.site-header.is-scrolled .nav-desktop__link:hover,
.site-header.always-scrolled .nav-desktop__link:hover {
  color: var(--color-accent);
}

.site-header.is-scrolled .nav-toggle__bar,
.site-header.always-scrolled .nav-toggle__bar {
  background-color: var(--color-text-primary);
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  max-width: var(--container-max);
  margin: 0 auto;
  padding: 0 var(--container-padding);
}

/* ---- Logo ---- */
.site-logo {
  display: flex;
  flex-direction: column;
  text-decoration: none;
  line-height: 1;
}

.site-logo__sub {
  font-family: var(--font-display);
  font-size: 0.55rem;
  font-weight: var(--fw-light);
  letter-spacing: var(--ls-ultra);
  text-transform: uppercase;
  color: rgba(255, 255, 255, 0.7);
  margin-bottom: 2px;
  transition: color var(--duration-normal) var(--ease-out);
}

.site-logo__main {
  font-family: var(--font-display);
  font-size: clamp(1.4rem, 2.5vw, 1.8rem);
  font-weight: var(--fw-regular);
  letter-spacing: 0.06em;
  color: #fff;
  transition: color var(--duration-normal) var(--ease-out);
}

.site-logo:hover .site-logo__main {
  color: var(--color-accent);
}

/* ---- Desktop Navigation ---- */
.nav-desktop {
  display: flex;
  align-items: center;
  gap: var(--space-xl);
}

.nav-desktop__link {
  font-family: var(--font-display);
  font-size: 0.75rem;
  font-weight: var(--fw-regular);
  letter-spacing: var(--ls-ultra);
  text-transform: uppercase;
  color: rgba(255, 255, 255, 0.7);
  position: relative;
  padding: 0.3em 0;
  transition: color var(--duration-normal) var(--ease-out);
}

.nav-desktop__link::after {
  content: '';
  position: absolute;
  bottom: -2px;
  left: 0;
  width: 0;
  height: 1px;
  background-color: var(--color-accent);
  transition: width var(--duration-normal) var(--ease-out);
}

.nav-desktop__link:hover {
  color: var(--color-accent);
}

.nav-desktop__link:hover::after,
.nav-desktop__link.is-active::after {
  width: 100%;
}

.nav-desktop__link.is-active {
  color: var(--color-accent);
}


/* ---- Mobile Hamburger Button ---- */
.nav-toggle {
  display: none;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  width: 40px;
  height: 40px;
  background: none;
  border: none;
  cursor: pointer;
  z-index: 1100;
  position: relative;
}

.nav-toggle__bar {
  display: block;
  width: 24px;
  height: 1px;
  background-color: #fff;
  transition:
    transform var(--duration-normal) var(--ease-out),
    opacity var(--duration-fast) var(--ease-out);
}

.nav-toggle__bar + .nav-toggle__bar {
  margin-top: 7px;
}

/* Hamburger → X animation */
.nav-toggle.is-open .nav-toggle__bar:nth-child(1) {
  transform: translateY(8px) rotate(45deg);
}

.nav-toggle.is-open .nav-toggle__bar:nth-child(2) {
  opacity: 0;
}

.nav-toggle.is-open .nav-toggle__bar:nth-child(3) {
  transform: translateY(-8px) rotate(-45deg);
}


/* ---- Mobile Fullscreen Overlay ---- */
.nav-mobile-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background-color: rgba(255, 255, 255, 0.97);
  backdrop-filter: blur(30px);
  -webkit-backdrop-filter: blur(30px);
  z-index: 1050;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: var(--space-xl);
  opacity: 0;
  visibility: hidden;
  transition:
    opacity var(--duration-slow) var(--ease-out),
    visibility var(--duration-slow) var(--ease-out);
}

.nav-mobile-overlay.is-open {
  opacity: 1;
  visibility: visible;
}

/* メニューが開いているときのハンバーガーアイコンは黒にする */
.nav-toggle.is-open .nav-toggle__bar {
  background-color: var(--color-text-primary);
}

.nav-mobile-overlay__link {
  font-family: var(--font-display);
  font-size: clamp(1.4rem, 4vw, 2rem);
  font-weight: var(--fw-light);
  letter-spacing: var(--ls-ultra);
  text-transform: uppercase;
  color: var(--color-text-secondary);
  transition: color var(--duration-normal) var(--ease-out);
  opacity: 0;
  transform: translateY(20px);
}

.nav-mobile-overlay.is-open .nav-mobile-overlay__link {
  opacity: 1;
  transform: translateY(0);
  transition:
    opacity var(--duration-slow) var(--ease-out),
    transform var(--duration-slow) var(--ease-out),
    color var(--duration-normal) var(--ease-out);
}

/* Stagger animation for mobile links */
.nav-mobile-overlay.is-open .nav-mobile-overlay__link:nth-child(1) { transition-delay: 100ms; }
.nav-mobile-overlay.is-open .nav-mobile-overlay__link:nth-child(2) { transition-delay: 180ms; }
.nav-mobile-overlay.is-open .nav-mobile-overlay__link:nth-child(3) { transition-delay: 260ms; }
.nav-mobile-overlay.is-open .nav-mobile-overlay__link:nth-child(4) { transition-delay: 340ms; }
.nav-mobile-overlay.is-open .nav-mobile-overlay__link:nth-child(5) { transition-delay: 420ms; }

.nav-mobile-overlay__link:hover {
  color: var(--color-accent);
}


/* ---- Responsive ---- */
@media (max-width: 768px) {
  .nav-desktop {
    display: none;
  }

  .nav-toggle {
    display: flex;
  }

  .nav-mobile-overlay {
    display: flex;
  }
}