Angular Material拖放多个元素

Question

我正在尝试使用cdk进行多项目拖放。
选择多个项目并且开始拖动时，我不知道如何解决预览问题。
我已经解决了打字稿中的多项行为。
我不知道如何在html和css中修复预览。

单个项目预览一切正常

单个项目html

  <div cdkDropList class="list" (cdkDropListDropped)="drop($event)">
    <div
      [ngClass]="movie.checked ?  'item-selected' : 'item'"
      *ngFor="let movie of (movies$ | async); let i = index"
      cdkDrag
      (click)="onTouch($event, i)"
    >
      <div class="item-placeholder" *cdkDragPlaceholder>{{movie.name}}</div>
      {{movie.name}}
    </div>
  </div>

多个项目预览错误

  <div cdkDropList class="list" (cdkDropListDropped)="drop($event)">
    <div
      [ngClass]="movie.checked ?  'item-selected' : 'item'"
      *ngFor="let movie of (movies$ | async); let i = index"
      cdkDrag
      (click)="onTouch($event, i)"
      (cdkDragStarted)="dragStarted($event, i)"
    >
      <div class="item-placeholder" *cdkDragPlaceholder>
        <ng-container *ngIf="(selectedMovies$ | async).length > 0 else single">
          <div *ngFor="let selectedMovie of (selectedMovies$ | async)">
            {{selectedMovie.name}}
          </div>
        </ng-container>

        <ng-template #single>
          <div>{{movie.name}}</div>
        </ng-template>
      </div>

      <div *ngIf="!(isDragging && movie.checked)">
        {{movie.name}}
      </div>

    </div>
  </div>

.list {
  margin-bottom: 20px;
  width: 500px;
  max-width: 100%;
  border: solid 1px #ccc;
  /*min-height: 60px;*/
  height: 700px;
  display: block;
  background: white;
  border-radius: 4px;
  overflow: hidden;
}

.item {
  padding: 20px 10px;
  border-bottom: solid 1px #ccc;
  color: rgba(0, 0, 0, 0.87);
  display: flex;
  flex-direction: row;
  align-items: center;
  justify-content: space-between;
  box-sizing: border-box;
  cursor: move;
  background: white;
  font-size: 14px;
  /*height: 700px;*/
}

.item-selected {
  background-color: lime;
  padding: 20px 10px;
  border-bottom: solid 1px #ccc;
  color: rgba(0, 0, 0, 0.87);
  display: flex;
  flex-direction: row;
  align-items: center;
  justify-content: space-between;
  box-sizing: border-box;
  cursor: move;
  /*background: white;*/
  font-size: 14px;
  /*height: 700px;*/
}

.cdk-drag-preview {
  box-sizing: border-box;
  border-radius: 4px;
  box-shadow: 0 5px 5px -3px rgba(0, 0, 0, 0.2),
  0 8px 10px 1px rgba(0, 0, 0, 0.14),
  0 3px 14px 2px rgba(0, 0, 0, 0.12);
}

.cdk-drag-animating {
  transition: transform 250ms cubic-bezier(0, 0, 0.2, 1);
}

.item-placeholder {
  background: #ccc;
  border: dotted 3px #999;
  min-height: 60px;
  transition: transform 250ms cubic-bezier(0, 0, 0.2, 1);
}