/* ============================================================
   KOSEN HEADER — 高専LP専用ダークヘッダー
   GuildBord風ダークテーマ。共通header.cssとは完全独立。
   BEM: .kosen-header__xxx / .kosen-mobile-menu__xxx
   作成: 2026/04/08 — K1タスク
   ============================================================ */

/* ---- Kosen-local color tokens ---- */
.kosen-header,
.kosen-mobile-menu {
  --kosen-cyan: #00BCD4;
  --kosen-cyan-light: #26C6DA;
  --kosen-cyan-glow: rgba(0, 188, 212, 0.3);
  --kosen-dark: #0A0E1A;
  --kosen-dark-mid: #111827;
}

/* ============================================================
   HEADER BAR
   ============================================================ */
.kosen-header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: var(--z-header, 100);
  background: transparent;
  transition:
    background 0.5s var(--ease-smooth, ease),
    backdrop-filter 0.5s,
    box-shadow 0.5s;
}

.kosen-header.is-scrolled {
  background: rgba(10, 14, 26, 0.92);
  backdrop-filter: blur(24px);
  -webkit-backdrop-filter: blur(24px);
  box-shadow: 0 1px 0 rgba(255, 255, 255, 0.06);
}

.kosen-header__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: var(--s-header-h, 72px);
  max-width: 1400px;
  margin: 0 auto;
  padding: 0 var(--s-gutter, 24px);
}

/* ---- Logo ---- */
.kosen-header__logo {
  display: flex;
  align-items: center;
  flex-shrink: 0;
  text-decoration: none;
}

.kosen-header__logo-img {
  height: 28px;
  width: auto;
  transition: opacity 0.3s;
}

/* ---- Nav ---- */
.kosen-header__nav {
  display: flex;
  align-items: center;
  gap: 36px;
}

.kosen-header__nav-list {
  display: flex;
  align-items: center;
  gap: 36px;
  list-style: none;
  margin: 0;
  padding: 0;
}

.kosen-header__nav-link {
  font-size: 13px;
  font-weight: 500;
  color: rgba(255, 255, 255, 0.9);
  letter-spacing: 0.02em;
  text-decoration: none;
  transition: color 0.3s;
  position: relative;
}

.kosen-header__nav-link::after {
  content: '';
  position: absolute;
  bottom: -4px;
  left: 0;
  width: 0;
  height: 1.5px;
  background: var(--kosen-cyan);
  transition: width 0.3s var(--ease-out, ease);
}

.kosen-header__nav-link:hover {
  color: var(--kosen-cyan-light);
}

.kosen-header__nav-link:hover::after {
  width: 100%;
}

.kosen-header__nav-link.is-active {
  color: var(--kosen-cyan);
}

.kosen-header__nav-link.is-active::after {
  width: 100%;
}

/* ---- CTA ---- */
.kosen-header__cta {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 10px 24px;
  border-radius: 6px;
  font-size: 12px;
  font-weight: 600;
  background: var(--kosen-cyan);
  color: #FFFFFF;
  letter-spacing: 0.02em;
  text-decoration: none;
  transition: all 0.3s var(--ease-out, ease);
}

.kosen-header__cta:hover {
  background: var(--kosen-cyan-light);
  transform: translateY(-1px);
  box-shadow: 0 4px 16px var(--kosen-cyan-glow);
}

.kosen-header__cta i {
  font-size: 14px;
}

/* ---- Hamburger ---- */
.kosen-header__hamburger {
  display: none;
  flex-direction: column;
  gap: 6px;
  padding: 8px;
  background: transparent;
  border: none;
  cursor: pointer;
  z-index: calc(var(--z-header, 100) + 1);
}

.kosen-header__hamburger span {
  width: 24px;
  height: 2px;
  background: rgba(255, 255, 255, 0.9);
  transition: transform 0.3s, opacity 0.3s;
  display: block;
}

.kosen-header__hamburger.is-active span:nth-child(1) {
  transform: translateY(8px) rotate(45deg);
}

.kosen-header__hamburger.is-active span:nth-child(2) {
  opacity: 0;
}

.kosen-header__hamburger.is-active span:nth-child(3) {
  transform: translateY(-8px) rotate(-45deg);
}

/* ============================================================
   MOBILE MENU
   ============================================================ */
.kosen-mobile-menu {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(10, 14, 26, 0.97);
  backdrop-filter: blur(24px);
  -webkit-backdrop-filter: blur(24px);
  z-index: var(--z-mobile-menu, 90);
  flex-direction: column;
  justify-content: center;
  align-items: center;
  gap: 8px;
  opacity: 0;
  visibility: hidden;
  transition: opacity 0.4s, visibility 0.4s;
}

.kosen-mobile-menu.is-open {
  opacity: 1;
  visibility: visible;
}

.kosen-mobile-menu__list {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
  list-style: none;
  margin: 0;
  padding: 0;
}

.kosen-mobile-menu__link {
  font-family: var(--f-heading-ja, 'Noto Serif JP', serif);
  font-size: 20px;
  font-weight: 500;
  color: rgba(255, 255, 255, 0.9);
  letter-spacing: 0.05em;
  text-decoration: none;
  padding: 12px 24px;
  transition: color 0.3s;
}

.kosen-mobile-menu__link:hover {
  color: var(--kosen-cyan-light);
}

/* モバイルメニュー内のCTAボタンは非表示（ヘッダー右上のCTAと重複するため） */
.kosen-mobile-menu__list > li:has(.kosen-mobile-menu__link--cta) {
  display: none;
}

/* ============================================================
   RESPONSIVE
   ============================================================ */
@media (max-width: 768px) {
  .kosen-header__nav {
    display: none;
  }

  .kosen-header__hamburger {
    display: flex;
  }

  .kosen-mobile-menu {
    display: flex;
  }

  .kosen-header__inner {
    padding: 0 16px;
  }

  .kosen-header__logo-img {
    height: 24px;
  }
}

/* ============================================================
   ACCESSIBILITY: prefers-reduced-motion
   ============================================================ */
@media (prefers-reduced-motion: reduce) {
  .kosen-header,
  .kosen-header__nav-link::after,
  .kosen-header__cta,
  .kosen-mobile-menu,
  .kosen-header__hamburger span {
    transition: none;
  }
}