.gw-back-to-top {
  position: fixed;
  z-index: 9;
  right: max(24px, env(safe-area-inset-right));
  bottom: max(24px, env(safe-area-inset-bottom));
  display: grid;
  place-items: center;
  box-sizing: border-box;
  width: 44px;
  height: 44px;
  margin: 0;
  padding: 0;
  border: 0;
  border-radius: 10px;
  background: var(--black, #262626);
  color: var(--white, #eeeeee);
  box-shadow: 0 3px 12px rgba(0, 0, 0, .15);
  cursor: pointer;
  appearance: none;
  opacity: 0;
  visibility: hidden;
  pointer-events: none;
  transform: translateY(6px);
  transition: opacity .25s ease, transform .25s ease, color .2s ease, visibility 0s linear .25s;
  -webkit-tap-highlight-color: transparent;
}

.gw-back-to-top[hidden] { display: none; }

.gw-back-to-top.is-visible {
  opacity: 1;
  visibility: visible;
  pointer-events: auto;
  transform: translateY(0);
  transition-delay: 0s;
}

.gw-back-to-top svg { display: block; width: 22px; height: 22px; }

@media (hover: hover) {
  .gw-back-to-top:hover { color: var(--accent, #ff9600); }
}

.gw-back-to-top:focus-visible {
  color: var(--accent, #ff9600);
  outline: 2px solid var(--accent, #ff9600);
  outline-offset: 4px;
}

/* スマホメニューを開いている間は表示しない。 */
body.menu-open .gw-back-to-top { display: none; }

@media (max-width: 767px) {
  .gw-back-to-top {
    right: max(16px, env(safe-area-inset-right));
    bottom: max(16px, env(safe-area-inset-bottom));
  }
}

@media (prefers-reduced-motion: reduce) {
  .gw-back-to-top { transition: none; transform: none; }
}