ul,li加css的:hover完成级联选择(不使用js)

三级级联选择，如图所示

思路：ul里面包li再包ul再包li再包ul再包li

html代码

<ul class="Aul">
    <li class="Ali">
        <span>一级菜单a</span>
        <ul class="Bul">
            <li class="Bli">
                <span>二级菜单a</span>
                <ul class="Cul">
                    <li class="Cli">
                        <span>三级菜单a</span>
                    </li>
                    <li class="Cli">
                        <span>三级菜单b</span>
                    </li>
                </ul>
            </li>
            <li class="Bli">
                <span>二级菜单b</span>
                <ul class="Cul">
                    <li class="Cli">
                        <span>三级菜单a</span>
                    </li>
                    <li>
                        <span>三级菜单b</span>
                    </li>
                </ul>
            </li>
        </ul>
    </li>
    <li>
        <span>一级菜单b</span>
        <ul>...</ul>
    </li>
    <li>
        <span>一级菜单c</span>
        <ul>...</ul>
    </li>
</ul>