#backToTop {
  position: fixed;
  bottom: 25vh;
  right: 5vw;
  width: 56px;        /* 更大点击区 */
  height: 56px;
  background-color: #dc3545;
  color: white;
  border: none;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  box-shadow: 0 4px 8px rgba(0, 0, 0, 0.25);
  opacity: 0;
  visibility: hidden;
  z-index: 9999;
  transition: opacity 0.3s ease, visibility 0.3s ease, background-color 0.3s ease;
}

#backToTop:hover {
  background-color: #a71d2a;
}

@media (max-width: 768px) {
  #backToTop {
    width: 50px;
    height: 50px;
  }
}

@media (max-width: 480px) {
  #backToTop {
    width: 44px;
    height: 44px;
  }
}

#backToTop svg {
  width: 24px;
  height: 24px;
}