#backToTop {
  position: fixed;
  right: max(24px, env(safe-area-inset-right));
  bottom: calc(24px + env(safe-area-inset-bottom, 0px));
  z-index: 1000;
  box-sizing: border-box;
  display: flex;
  align-items: center;
  justify-content: center;
  width: 48px;
  height: 48px;
  padding: 0;
  border: 1px solid #c0392b;
  border-radius: 50%;
  background: #2b2b2b;
  color: #f7f5f0;
  box-shadow: 0 4px 12px rgb(0 0 0 / 15%);
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  pointer-events: none;
  transition: opacity .3s ease, visibility .3s ease, transform .2s ease, background-color .2s ease;
}

#backToTop .btn-text {
  writing-mode: vertical-rl;
  font-family: "Yu Mincho", "游明朝", "Hiragino Mincho ProN", "MS P明朝", serif;
  font-size: 13px;
  letter-spacing: 2px;
  line-height: 1;
}

#backToTop.show {
  opacity: 1;
  visibility: visible;
  pointer-events: auto;
}

@media (hover: hover) {
  #backToTop:hover {
    background: #c0392b;
    color: #fff;
    transform: translateY(-3px);
  }
}

#backToTop:focus-visible {
  outline: 3px solid #c0392b;
  outline-offset: 4px;
}

@media (max-width: 768px) {
  #backToTop {
    right: max(16px, env(safe-area-inset-right));
    bottom: calc(16px + env(safe-area-inset-bottom, 0px));
    width: 44px;
    height: 44px;
  }
  #backToTop .btn-text { font-size: 12px; }
}

@media (prefers-reduced-motion: reduce) {
  #backToTop { transition: none; }
  #backToTop:hover { transform: none; }
}

@media print {
  #backToTop { display: none; }
}