element-ui elemant-plus el-tree展开按钮变成加减号

效果：

css 直接加上就可以用了，如果要加在公共样式里面的话把 ::v-deep 都去掉就可以了：

.el-tree ::v-deep .el-tree-node__expand-icon.expanded {
  -webkit-transform: rotate(0deg);
  transform: rotate(0deg);
}
//有子节点 且未展开
.el-tree ::v-deep .el-icon-caret-right:before {
  background: url("../../assets/img/add.png") no-repeat 0;
  content: "";
  display: block;
  width: 16px;
  height: 16px;
  font-size: 16px;
  background-size: 16px;
}
//有子节点 且已展开
.el-tree
  ::v-deep
  .el-tree-node__expand-icon.expanded.el-icon-caret-right:before {
  background: url("../../assets/img/del.png") no-repeat 0;
  content: "";
  display: block;
  width: 16px;
  height: 16px;
  font-size: 16px;
  background-size: 16px;
}
//没有子节点
.el-tree ::v-deep .el-tree-node__expand-icon.is-leaf::before {
  background: url("../../assets/img/del.png") no-repeat 0;
  content: "";
  display: block;
  width: 16px;
  height: 16px;
  font-size: 16px;
  background-size: 16px;
}

加减号icon图片：

用vue3+elementPlus的时候上面样式有一点问题，稍微改了一下：

:deep(.el-tree-node__content > .el-tree-node__expand-icon) {
  width: 14px;
}
.el-tree :deep(.el-tree-node__expand-icon.expanded) {
  -webkit-transform: rotate(0deg);
  transform: rotate(0deg);
}
//有子节点 且未展开
.el-tree :deep(.el-tree-node__expand-icon:before) {
  background: url("../../../assets/images/add.png") no-repeat 0;
  content: "";
  display: block;
  width: 16px;
  height: 16px;
  font-size: 16px;
  background-size: 16px;
}
:deep(.el-icon svg) {
  display: none;
}
//有子节点 且已展开
.el-tree :deep(.el-tree-node__expand-icon.expanded:before) {
  background: url("../../../assets/images/del.png") no-repeat 0;
  content: "";
  display: block;
  width: 16px;
  height: 16px;
  font-size: 16px;
  background-size: 16px;
}
//没有子节点
.el-tree :deep(.el-tree-node__expand-icon.is-leaf::before) {
  background: none;
  content: "";
  display: block;
  width: 16px;
  height: 16px;
  font-size: 16px;
  background-size: 16px;
}