element-ui/examples/demo-styles/tree.scss

.demo-tree {
  .leaf {
    width: 20px;
    background: #ddd;
  }

  .folder {
    width: 20px;
    background: #888;
  }

  .buttons {
    margin-top: 20px;
  }

  .filter-tree {
    margin-top: 20px;
  }

  .custom-tree-container {
    display: flex;
    margin: -24px;
  }

  .block {
    flex: 1;
    padding: 8px 24px 24px;

    &:first-child {
      border-right: solid 1px #eff2f6;
    }

    > p {
      text-align: center;
      margin: 0;
      line-height: 4;
    }
  }

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