Detailed explanation of adding dotted lines to Vue element tree controls

   <div class="mytree">
          <!--indent can only be 0-->
          <el-tree
              :data="tree_data"
              :props="defaultProps"
              @node-click="handleNodeClick"
              indent="0"
              :render-content="renderContent"
          ></el-tree>
   </div>

<style lang="scss" scoped>
::v-deep .mytree {
  .el-tree > .el-tree-node:after {
    border-top: none;
  }
  .el-tree-node {
    position: relative;
    padding-left: 16px;
  }
  //There is a gap between nodes, just hide the expand button, if you think the gap is okay, you can delete it.el-tree-node__expand-icon.is-leaf{
    display: none;
  }
  .el-tree-node__children {
    padding-left: 16px;
  }
  .el-tree-node :last-child:before {
    height: 38px;
  }
  .el-tree > .el-tree-node:before {
    border-left: none;
  }
  .el-tree > .el-tree-node:after {
    border-top: none;
  }
  .el-tree-node:before {
    content: "";
    left: -4px;
    position: absolute;
    right: auto;
    border-width: 1px;
  }
  .el-tree-node:after {
    content: "";
    left: -4px;
    position: absolute;
    right: auto;
    border-width: 1px;
  }
  .el-tree-node:before {
    border-left: 1px dashed #4386c6;
    bottom: 0px;
    height: 100%;
    top: -26px;
    width: 1px;
  }
  .el-tree-node:after {
    border-top: 1px dashed #4386c6;
    height: 20px;
    top: 12px;
    width: 24px;
  }
}
</style>