hac/src/styles/app/tools.scss

//树的虚线
@mixin elTreeNodeChildren() {
    $name: '.el-tree-node__children';
    @for $i from 1 to 20 {
        #{$name} {
            &:before {
                left: calc(11.5px + (#{$i - 1} * 18px));
            }
        }
        $name: '#{$name} .el-tree-node__children';
    }
}