message: fix(BackTop): failed to get element ref
diff: @@ -95,11 +95,10 @@ export default defineComponent({
  onMounted(() => {
  nextTick(() => {
  if (inBrowser) {
  - scrollParent.value = document.documentElement;
  target = props.target
  ? (getTarget() as typeof target)
  : (getScrollParent(backTopEl.value!) as typeof target);
  - scrollParent.value = target as typeof target;
  + scrollParent.value = target;
  }
  });
  });
  @@ -107,7 +106,7 @@ export default defineComponent({
  return () => {
  const Content = (
  <div
  - ref="backTopEl"
  + ref={backTopEl}
  class={bem({ active: show.value })}
  style={backTopStyle.value}
  onClick={onClick}
  