.video-lists ul li a .pic:after {
  background: url(images/sp_btn.png) no-repeat center;
  width: 0.5rem;
  height: 0.5rem;
  background-size: 100%;
  left: calc(50% - 0.25rem);
  top: calc(50% - 0.25rem);
  position: absolute;
  content: "";}