纯css实现属性结构

**css实现属性结构的思路是利用伪类实现树形结构连接线，如果想实现点击展开和收

缩以及复选框效果还得配合js来实现。其实展开和收缩就是一个点击元素其子元素隐藏

和显示的切换。**

效果图

html结构

    <ul class="domtree">

        <li>

            1级菜单

            <ul>

                <li>2级菜单</li>

                <li>

                    2级菜单

                    <ul>

                        <li>3级菜单</li>

                        <li>3级菜单</li>

                    </ul>

                </li>

            </ul>

        </li>

        <li>

            1级菜单

            <ul>

                <li>2级菜单</li>

                <li>2级菜单</li>

            </ul>

        </li>

    </ul>

css

        ul.domtree,

        ul.domtree ul {

            margin: 0;

            padding: 0 0 0 2em;

        }

        ul.domtree li {

            list-style: none;

            position: relative;

        }

        ul.domtree>li:first-child:before {

            border-style: none none solid none;

        }

        ul.domtree li:before {

            position: absolute;

            content: '';

            top: -0.01em;

            left: -0.7em;

            width: 0.5em;

            height: 0.615em;

            border-style: none none solid solid;

            border-width: 0.05em;

            border-color: #aaa;

        }

        ul.domtree li:not(:last-child):after {

            position: absolute;

            content: '';

            top: 0.7em;

            left: -0.7em;

            bottom: 0;

            border-style: none none none solid;

            border-width: 0.05em;

            border-color: #aaa;

        }