修改el-tree箭头为加减符号

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

原文