element-plus/docs/examples/tree/custom-node-class.vue

<template>
  <div class="custom-tree-node-container">
    <el-tree
      :data="data"
      show-checkbox
      node-key="id"
      default-expand-all
      :expand-on-click-node="false"
      :props="{ class: customNodeClass }"
    />
  </div>
</template>

<script lang="ts" setup>
import type Node from 'element-plus/es/components/tree/src/model/node'

interface Tree {
  id: number
  label: string
  isPenultimate?: boolean
  children?: Tree[]
}

const customNodeClass = (data: Tree, node: Node) => {
  if (data.isPenultimate) {
    return 'is-penultimate'
  }
  return null
}

const data: Tree[] = [
  {
    id: 1,
    label: 'Level one 1',
    children: [
      {
        id: 4,
        label: 'Level two 1-1',
        isPenultimate: true,
        children: [
          {
            id: 9,
            label: 'Level three 1-1-1',
          },
          {
            id: 10,
            label: 'Level three 1-1-2',
          },
        ],
      },
    ],
  },
  {
    id: 2,
    label: 'Level one 2',
    isPenultimate: true,
    children: [
      {
        id: 5,
        label: 'Level two 2-1',
      },
      {
        id: 6,
        label: 'Level two 2-2',
      },
    ],
  },
  {
    id: 3,
    label: 'Level one 3',
    isPenultimate: true,
    children: [
      {
        id: 7,
        label: 'Level two 3-1',
      },
      {
        id: 8,
        label: 'Level two 3-2',
      },
    ],
  },
]
</script>

<style>
.is-penultimate > .el-tree-node__content {
  color: red;
}

.el-tree-node.is-expanded.is-penultimate > .el-tree-node__children {
  display: flex;
  flex-direction: row;
}
.is-penultimate > .el-tree-node__children > div {
  width: 25%;
}
</style>