要替换的图标
::v-deep .el-table__column-filter-trigger .el-icon-arrow-down {
  //替换图片地址
  background: url('../../../../../assets/icon/bg-screen.png') center center
    no-repeat;
  background-size: 20px;
}
::v-deep .el-table__column-filter-trigger .el-icon-arrow-down::before {
  //占位
  content: '替';
  font-size: 16px;
  visibility: hidden;
}

给元素添加图标

//el-tree-node__label 要给添加图标的元素
::v-deep .el-tree-node__label {
  /* 保证:after为元素的显示 */
  background-image: url('');
}
::v-deep .el-tree-node__label:after {
  display: inline-block;
  background-image: url('../../assets/icon/caidan.png');
  background-position: center center;
  background-size: 40px 20px;
  content: '';
  width: 40px;
  height: 20px;
  /* visibility: hidden; 隐藏content中的内容*/
  margin-left: 280px;
}