/* Shared back-to-top control used across the site's primary pages. */
#backToTop {
  position: fixed;
  bottom: max(18px, env(safe-area-inset-bottom));
  right: auto;
  left: clamp(
    var(--control-card-inset, 18px),
    calc(50% + var(--control-card-width, 980px) / 2 + var(--control-card-gap, 12px)),
    calc(100vw - 72px - max(var(--control-card-inset, 18px), env(safe-area-inset-right)))
  );
  z-index: 9999;
  background: rgba(110, 201, 255, 0.5);
  color: #fff;
  padding: 12px 18px;
  border-radius: 50px;
  font-size: 24px;
  text-decoration: none;
  box-shadow: 0 4px 12px rgba(0,0,0,0.2);
  opacity: 0;
  transition: opacity 0.3s ease;
}

#backToTop.show {
  opacity: 1;
}

.top-icon {
  display: inline-block;
  font-size: 36px;
  line-height: 1;
}

@media (max-width: 600px) {
  #backToTop {
    bottom: max(8px, env(safe-area-inset-bottom));
  }
}