/* ============================================================
   浮動側欄 + 回頂按鈕 Floating Nav
   來源 style.css 行 3901-3994（純搬移，內容未改）
   ============================================================ */

/* ============================================================
   FLOATING NAV + BACK TO TOP
   ============================================================ */
/* 軌道：absolute 限定於 hero 之後到 body 底，內部 .floating-nav 以 sticky 在此範圍黏附垂直置中 */
/* top 取 100vh 與 1500px（.hero min-height）較大者，避免低視窗高度時 sticky 提早出現於 hero 內 */
.floating-nav-rail {
  position: absolute;
  left: 0;
  top: max(100vh, 1500px);
  bottom: 0;
  width: 0;
  pointer-events: none;
  z-index: 80;
}

.floating-nav {
  position: sticky;
  top: 50%;
  transform: translateY(-50%);
  width: 86px;
  background: rgba(255, 255, 255, .55);
  backdrop-filter: blur(28px) saturate(180%);
  -webkit-backdrop-filter: blur(28px) saturate(180%);
  border-radius: 0 32px 32px 0;
  padding: 14px 0;
  display: flex;
  flex-direction: column;
  box-shadow: 4px 4px 20px rgba(0, 0, 0, .08);
  border: 1px solid rgba(255, 255, 255, .8);
  border-left: 0;
  /* 預設隱藏：滾到關於區塊才由 JS 加上 .is-visible 顯示，超過聯絡區塊再隱藏 */
  opacity: 0;
  visibility: hidden;
  pointer-events: none;
  /* 深淺切換 + 顯示/隱藏平滑過渡（與主選單一致） */
  transition: background .3s ease, border-color .3s ease, box-shadow .3s ease, opacity .3s ease, visibility .3s ease;
}

/* RWD（原 4011-4013）*/
@media (max-width: 1599px) {
  .floating-nav {
    display: none !important;
  }
}

/* 進入關於～聯絡區塊範圍時顯示 */
.floating-nav.is-visible {
  opacity: 1;
  visibility: visible;
  pointer-events: auto;
}

.floating-nav a {
  font-family: var(--f-body);
  font-weight: 500;
  font-size: var(--fs-xs);
  color: rgba(34, 34, 34, .45);
  letter-spacing: .5px;
  text-align: center;
  line-height: 1.3;
  padding: 18px 10px;
  border-bottom: 1px solid rgba(0, 0, 0, .06);
  transition: color .25s, transform .25s, border-color .3s ease;
}

.floating-nav a:last-child {
  border-bottom: 0;
}

.floating-nav a:hover {
  color: var(--c-brand);
}

.floating-nav a.is-active {
  color: var(--c-text);
  font-weight: 700;
}

/* ============================================================
   深色區塊變體（與主選單同邏輯）
   側欄中心位於 data-header-mode="dark" 區塊時，由 JS init_floating_nav 加上 .is-dark
   淺色區塊 → 白底黑字（預設）；深色區塊 → 黑底白字
   ============================================================ */
.floating-nav.is-dark {
  background: rgba(60, 60, 60, .45);
  border-color: rgba(255, 255, 255, .18);
  box-shadow: 4px 4px 20px rgba(0, 0, 0, .25);
}

.floating-nav.is-dark a {
  color: rgba(255, 255, 255, .55);
  border-bottom-color: rgba(255, 255, 255, .12);
}

.floating-nav.is-dark a:hover {
  color: var(--c-brand);
}

.floating-nav.is-dark a.is-active {
  color: var(--c-on-dark);
}

.back-to-top {
  position: fixed;
  right: 24px;
  bottom: 24px;
  z-index: 80;
  width: 56px;
  height: 56px;
  border-radius: var(--r-full);
  color: var(--c-on-dark);
  font-family: var(--f-display);
  font-weight: 700;
  font-size: 12px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  box-shadow: var(--sh-cta);
  opacity: 0;
  pointer-events: none;
  transform: translateY(12px);
  transition: opacity .3s, transform .3s;
  letter-spacing: 1px;
}

.back-to-top.show {
  opacity: 1;
  pointer-events: auto;
  transform: translateY(0);
}

.back-to-top:hover {
  background: var(--c-brand-hover);
  color: var(--c-on-dark);
}

#backToTop {
  cursor: pointer;
}

#backToTop:hover {
  opacity: 0.7;
}