直接css样式覆盖，不行的话需要在前面穿透样式。

.custom-tree-node {
  flex: 1;
  display: flex;
  align-items: center;
  justify-content: space-between;
  font-size: 14px;
  padding-right: 8px;
}

.el-tree {
  margin: 20px;
  border: solid 1px #d9d9d9;
  color: #1baaff;
  height: 810px;
  overflow-y: scroll;
}

.el-tree--highlight-current .el-tree-node.is-current > .el-tree-node__content {
  color: #fff;
  background-color: #1baaff;
}

.el-tree-node__content {
  line-height: 50px;
  height: 50px;
}

.el-tree-node__content > .el-tree-node__expand-icon {
  padding: 10px;
  content: url(../../assets/img/open.png)
}

.el-tree--highlight-current .el-tree-node.is-current > .el-tree-node__content > .el-tree-node__expand-icon {
  content: url(../../assets/img/open-w.png) !important;
}

.expanded {

  content: url(../../assets/img/awope-b.png) !important;
}

.el-tree--highlight-current .el-tree-node.is-current > .el-tree-node__content > .expanded {
  content: url(../../assets/img/awopne.png) !important;
}

.el-tree--highlight-current .el-tree-node.is-current > .el-tree-node__content > .is-leaf,
.is-leaf {
  content: '' !important;
}