.scroll-to-top-btn {
  position: fixed;
  z-index: 9999;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  background-color: rgb(var(--color-button-background));
  color: rgb(var(--color-button-text));
  border: none;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: rgba(0, 0, 0, 0.3) 1px 1px 10px 0px;
  transition: all 0.3s ease;
}

.scroll-to-top-btn:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.2);
  opacity: 0.9;
}

.scroll-to-top-btn svg {
  display: block;
}

/* 位置 */
.scroll-to-top-btn--bottom-left {
  bottom: var(--offset-y);
  left: var(--offset-x);
}

.scroll-to-top-btn--bottom-right {
  bottom: calc(var(--offset-y) + var(--sticky-atc-offset));
  right: var(--offset-x);
}

.scroll-to-top-btn--bottom-center {
  bottom: var(--offset-y);
  left: 50%;
  transform: translateX(-50%);
}

.scroll-to-top-btn--bottom-center:hover {
  transform: translateX(-50%) translateY(-2px);
}

/* 移动端调整 */
@media (max-width: 749px) {
  .scroll-to-top-btn {
    width: 44px;
    height: 44px;
  }

  .scroll-to-top-btn svg {
    width: 18px;
    height: 18px;
  }
}