/* ========================================
   Back to Top Component
   返回頂部按鈕
   ======================================== */

.back-to-top {
  position: fixed;
  bottom: 24px;
  right: 24px;
  width: 48px;
  height: 48px;
  border-radius: 50%;
  background: linear-gradient(135deg, var(--color-primary), var(--color-secondary));
  color: #FFFFFF;
  border: none;
  cursor: pointer;
  box-shadow: var(--shadow-lg);
  opacity: 0;
  visibility: hidden;
  transform: translateY(20px);
  transition: opacity var(--transition), transform var(--transition), visibility var(--transition);
  z-index: 110;
  display: flex;
  align-items: center;
  justify-content: center;
}

.back-to-top--show {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

.back-to-top:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
}

.back-to-top:active {
  transform: scale(0.96);
}

.back-to-top:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
}