element-plus/website/demo-styles/transition.scss

.demo-transition {
  .transition-box {
    margin-bottom: 10px;
    width: 200px;
    height: 100px;
    border-radius: 4px;
    background-color: #409eff;
    text-align: center;
    color: #fff;
    padding: 40px 20px;
    margin-right: 20px;
    box-sizing: border-box;
  }
}