如何通过html和css完成下拉菜单的制作？

例如这种，当然这只是一个例子，其他的也行，如果可以，请简要说明一下用到哪些技能点和原理。

回复内容：

几个下拉菜单display:none
按钮 :hover 给下拉菜单display:block
也许可以 无脚本，纯HTML和 CSS 实现的多级下拉菜单，在非 IE 内核浏览器和 IE8+ 表现完美。



主体使用ul>li>ul>li>......嵌套定义多级。

<code class="language-html"><span class="cp">
<span class="nt"></span>
<span class="nt"></span>
  <span class="nt"><meta> <span class="na">http-equiv=</span><span class="s">"Content-Type"</span> <span class="na">content=</span><span class="s">"text/html; charset=utf-8"</span><span class="nt">></span>
  <span class="nt"><title></title></span>纯 CSS 多级菜单<span class="nt"></span>
  <span class="nt"><style></style></span>
    <span class="nc">.menu</span><span class="p">{}</span>
    <span class="nc">.menu</span> <span class="nt">ul</span><span class="o">,</span><span class="nc">.menu</span> <span class="nt">li</span><span class="p">{</span><span class="k">margin</span><span class="o">:</span><span class="m">0</span><span class="p">;</span> <span class="k">padding</span><span class="o">:</span><span class="m">0</span><span class="p">;</span><span class="k">list-style</span><span class="o">:</span><span class="k">none</span> <span class="k">outside</span><span class="p">;}</span>
    <span class="nc">.menu</span><span class="o">></span><span class="nt">ul</span><span class="p">{</span><span class="k">overflow</span><span class="o">:</span><span class="k">auto</span><span class="p">;</span> <span class="k">display</span><span class="o">:</span><span class="k">inline</span><span class="o">-</span><span class="k">block</span><span class="p">;}</span>
    <span class="nc">.menu</span> <span class="nt">a</span><span class="o">,</span><span class="nc">.menu</span> <span class="nt">span</span><span class="p">{</span> <span class="k">cursor</span><span class="o">:</span><span class="k">default</span><span class="p">;</span> <span class="k">height</span><span class="o">:</span><span class="m">30px</span><span class="p">;</span> <span class="k">line-height</span><span class="o">:</span><span class="m">30px</span><span class="p">;</span> <span class="k">padding</span><span class="o">:</span><span class="m">0</span> <span class="m">5px</span><span class="p">;</span> <span class="k">display</span><span class="o">:</span><span class="k">block</span><span class="p">;</span> <span class="k">text</span><span class="o">-</span><span class="k">overflow</span><span class="o">:</span><span class="n">ellipsis</span><span class="p">;</span> <span class="k">overflow</span><span class="o">:</span><span class="k">hidden</span><span class="p">;</span> <span class="k">text-decoration</span><span class="o">:</span><span class="k">none</span><span class="p">;</span> <span class="k">color</span><span class="o">:</span><span class="n">MenuText</span><span class="p">;}</span>
    <span class="nc">.menu</span> <span class="nt">a</span><span class="nd">:hover</span><span class="o">,</span><span class="nc">.menu</span> <span class="nt">span</span><span class="nd">:hover</span><span class="o">,</span><span class="nc">.menu</span> <span class="nt">li</span><span class="nd">:hover</span><span class="o">></span><span class="nt">a</span><span class="o">,</span><span class="nc">.menu</span> <span class="nt">li</span><span class="nd">:hover</span><span class="o">></span><span class="nt">span</span><span class="p">{</span><span class="k">color</span><span class="o">:</span><span class="n">HighlightText</span><span class="p">;}</span>
    <span class="nc">.menu</span> <span class="nt">li</span><span class="nd">:hover</span><span class="p">{</span><span class="k">background-color</span><span class="o">:</span><span class="n">Highlight</span><span class="p">;}</span>
    <span class="nc">.menu</span> <span class="nt">li</span><span class="nd">:hover</span><span class="o">></span><span class="nt">ul</span><span class="p">{</span><span class="k">display</span><span class="o">:</span><span class="k">block</span><span class="p">;}</span>
    <span class="nc">.menu</span><span class="o">></span><span class="nt">ul</span><span class="o">></span><span class="nt">li</span><span class="p">{</span><span class="k">float</span><span class="o">:</span><span class="k">left</span><span class="p">;}</span>
    <span class="nc">.menu</span><span class="o">></span><span class="nt">ul</span><span class="o">></span><span class="nt">li</span> <span class="nt">ul</span><span class="p">{</span><span class="k">display</span><span class="o">:</span><span class="k">none</span><span class="p">;</span><span class="k">float</span><span class="o">:</span><span class="k">left</span><span class="p">;</span> <span class="k">background-color</span><span class="o">:</span><span class="m">#fff</span><span class="p">;</span> <span class="k">border</span><span class="o">:</span><span class="m">1px</span> <span class="k">solid</span> <span class="n">Highlight</span><span class="p">;</span> <span class="k">position</span><span class="o">:</span><span class="k">absolute</span><span class="p">;}</span>
    <span class="nc">.menu</span><span class="o">></span><span class="nt">ul</span><span class="o">></span><span class="nt">li</span> <span class="nt">li</span><span class="p">{</span><span class="k">padding-left</span><span class="o">:</span><span class="m">25px</span><span class="p">;</span><span class="k">margin</span><span class="o">:</span><span class="m">2px</span><span class="p">;</span><span class="k">background</span><span class="o">:</span><span class="k">transparent</span> <span class="sx">url(data:image/gif;base64,R0lGODlhEAAQAIAAAJmZmf///yH5BAAAAAAALAAAAAAQABAAAAIjhI9pwe2+nmRRIQrmjBrmYB1Y93Ak+IXVd6LtiIZwa5JqWAAAOw==)</span> <span class="k">no-repeat</span> <span class="m">5px</span> <span class="k">center</span><span class="p">;</span> <span class="k">width</span><span class="o">:</span><span class="m">150px</span><span class="p">;}</span>
    <span class="nc">.menu</span><span class="o">></span><span class="nt">ul</span><span class="o">></span><span class="nt">li</span><span class="o">></span><span class="nt">ul</span><span class="o">></span><span class="nt">li</span> <span class="nt">ul</span><span class="p">{</span><span class="k">margin-left</span><span class="o">:</span><span class="m">140px</span><span class="p">;</span> <span class="k">margin-top</span><span class="o">:-</span><span class="m">30px</span><span class="p">;}</span>
    <span class="nc">.menu</span> <span class="nt">li</span><span class="nc">.expand</span><span class="o">></span><span class="nt">a</span><span class="o">,</span><span class="nc">.menu</span> <span class="nt">li</span><span class="nc">.expand</span><span class="o">></span><span class="nt">span</span><span class="p">{</span><span class="k">background</span><span class="o">:</span><span class="k">transparent</span> <span class="sx">url(data:image/png;base64,R0lGODlhAwAQAIABAAAAAP///yH5BAEAAAEALAAAAAADABAAAAIKjI8JBtv/wko0FQA7)</span> <span class="k">no-repeat</span> <span class="k">right</span> <span class="k">center</span><span class="p">;</span> <span class="k">padding-right</span><span class="o">:</span><span class="m">10px</span><span class="p">;</span> <span class="k">margin-right</span><span class="o">:</span><span class="m">5px</span><span class="p">;}</span>
    <span class="nc">.menu</span><span class="o">></span><span class="nt">ul</span><span class="o">></span><span class="nt">li</span><span class="nc">.expand</span><span class="o">></span><span class="nt">a</span><span class="o">,</span><span class="nc">.menu</span><span class="o">></span><span class="nt">ul</span><span class="o">></span><span class="nt">li</span><span class="nc">.expand</span><span class="o">></span><span class="nt">span</span><span class="p">{</span> <span class="k">background-image</span><span class="o">:</span><span class="sx">url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAYAAAADCAYAAACwAX77AAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsMAAA7DAcdvqGQAAAAaSURBVBhXY2BgYPiPAwOFMSXBgjAA0wnmAwASVQv19UVKmwAAAABJRU5ErkJggg==)</span><span class="p">;}</span>
  <span class="nt"></span>
<span class="nt"></span>

<span class="nt"></span>

  <span class="nt"><div> <span class="na">id=</span><span class="s">"mainnav"</span> <span class="na">class=</span><span class="s">"menu"</span><span class="nt">></span>
    <span class="nt"><ul></ul></span>
      <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
      <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
      <span class="nt"><li> <span class="na">class=</span><span class="s">"expand"</span><span class="nt">><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></span>
        <span class="nt"><ul></ul></span>
          <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
          <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
          <span class="nt"><li> <span class="na">class=</span><span class="s">"expand"</span><span class="nt">><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>很长很长很长很长很长很长很长很长很长很长<span class="nt"></span></a></span>
            <span class="nt"><ul></ul></span>
              <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
              <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
              <span class="nt"><li> <span class="na">class=</span><span class="s">"expand"</span><span class="nt">><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>LinkLink<span class="nt"></span></a></span>
                <span class="nt"><ul></ul></span>
                  <span class="nt"><li> <span class="na">class=</span><span class="s">"expand"</span><span class="nt">><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></span>
                    <span class="nt"><ul></ul></span>
                      <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
                      <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
                      <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
                      <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
                      <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
                    <span class="nt"></span>
                  <span class="nt"></span>
</li></span>
                  <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
                  <span class="nt"><li> <span class="na">class=</span><span class="s">"expand"</span><span class="nt">><span></span>span 菜单项<span class="nt"></span></span>
                    <span class="nt"><ul></ul></span>
                      <span class="nt"><li>
<span></span>span 菜单项<span class="nt"></span>
</li></span>
                      <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
                      <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
                      <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
                      <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
                    <span class="nt"></span>
                  <span class="nt"></span>
</li></span>
                  <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
                  <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
                <span class="nt"></span>
              <span class="nt"></span>
</li></span>
              <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
              <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
            <span class="nt"></span>
          <span class="nt"></span>
</li></span>
          <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
          <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
        <span class="nt"></span>
      <span class="nt"></span>
</li></span>
      <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
      <span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Link<span class="nt"></span></a></li></span>
    <span class="nt"></span>
  <span class="nt"></span>
</div></span>

<span class="nt"></span>
<span class="nt"></span>
</span></span></code>

既然你这么问了，我就当你是新手了，还好，我也是新手。

下面开说：
感觉用select标签效果好像不是很好，效果如下：
不如直接像 @周黎伟所说的，用一个button加上4个div

首先复习一下基本知识：
display：
所以这里我用inline－block

代码如下：

希望大神们能批评指正

最后的效果如图：

<code class="language-html"><span class="cp">
<span class="nt"> <span class="na">lang=</span><span class="s">"en"</span><span class="nt">></span>
<span class="nt"></span>
    <span class="nt"><meta> <span class="na">charset=</span><span class="s">"UTF-8"</span><span class="nt">></span>
    <span class="nt"><title></title></span>下拉菜单<span class="nt"></span>
    <span class="nt"><style><span class="na">type=</style></span><span class="s">"text/css"</span><span class="nt">></span>
    
    <span class="nc">.bt</span><span class="p">{</span>
        <span class="k">width</span><span class="o">:</span> <span class="m">50px</span><span class="p">;</span><span class="k">height</span><span class="o">:</span> <span class="m">28px</span><span class="p">;</span>
        <span class="k">border</span><span class="o">:</span> <span class="m">1px</span> <span class="k">solid</span> <span class="m">#ddd</span><span class="p">;</span>
        <span class="k">background-color</span><span class="o">:</span> <span class="m">#eee</span><span class="p">;</span>
        <span class="k">font</span><span class="o">:</span><span class="m">12px</span> <span class="s2">"宋体"</span><span class="p">;</span>
    <span class="p">}</span>
    <span class="nc">.ct</span><span class="p">{</span>
        <span class="k">display</span><span class="o">:</span> <span class="k">none</span><span class="p">;}</span>

    <span class="nc">.dt</span><span class="p">{</span>
        <span class="k">height</span><span class="o">:</span> <span class="m">30px</span><span class="p">;</span>
        <span class="k">margin-top</span><span class="o">:</span> <span class="m">0px</span><span class="p">;</span>
        <span class="k">border</span><span class="o">:</span> <span class="m">1px</span> <span class="k">solid</span> <span class="m">#ddd</span><span class="p">;</span>
        <span class="k">background-color</span><span class="o">:</span> <span class="nb">white</span><span class="p">;</span>
        <span class="k">padding</span><span class="o">:</span><span class="k">auto</span> <span class="m">10px</span><span class="p">;</span>
       <span class="p">}</span>

    <span class="nc">.dt1</span><span class="p">{</span>
        <span class="k">height</span><span class="o">:</span> <span class="m">30px</span><span class="p">;</span>
        <span class="k">margin-top</span><span class="o">:</span> <span class="m">1px</span><span class="p">;</span>
        <span class="k">border</span><span class="o">:</span> <span class="m">1px</span> <span class="k">solid</span> <span class="m">#ddd</span><span class="p">;</span>
        <span class="k">background-color</span><span class="o">:</span> <span class="nb">white</span><span class="p">;</span>
        <span class="k">padding</span><span class="o">:</span><span class="k">auto</span> <span class="m">10px</span><span class="p">;}</span>
 
    <span class="nc">.dt</span><span class="nd">:hover</span><span class="o">,</span><span class="nc">.dt1</span><span class="nd">:hover</span><span class="p">{</span><span class="k">background-color</span><span class="o">:</span> <span class="m">#ddd</span><span class="p">;}</span>
    <span class="nc">.bt</span><span class="nd">:hover</span><span class="p">{</span><span class="k">background-color</span><span class="o">:</span> <span class="nb">green</span><span class="p">;}</span>
    <span class="nc">.at</span><span class="nd">:hover</span> <span class="nc">.ct</span><span class="p">{</span><span class="k">display</span><span class="o">:</span> <span class="k">inline</span><span class="o">-</span><span class="k">block</span><span class="p">;}</span>
 
    <span class="nt"></span>
<span class="nt"></span>
<span class="nt"></span>
<span class="nt"><div> <span class="na">class=</span><span class="s">"at"</span><span class="nt">></span>
    <span class="nt"><div>
        <span class="nt"><button> <span class="na">class=</span><span class="s">"bt"</span> <span class="na">type=</span><span class="s">"button"</span> <span class="nt">></span>按钮<span class="nt"></span></button></span>
    <span class="nt"></span>
</div></span>
    <span class="nt"><div> <span class="na">class=</span><span class="s">"ct"</span> <span class="nt">></span>
        <span class="nt"><div> <span class="na">class=</span><span class="s">"dt1"</span><span class="nt">></span>下拉菜单<span class="nt"></span>
</div></span>
        <span class="nt"><div> <span class="na">class=</span><span class="s">"dt"</span><span class="nt">></span>下拉菜单<span class="nt"></span>
</div></span>
        <span class="nt"><div> <span class="na">class=</span><span class="s">"dt"</span><span class="nt">></span>下拉菜单<span class="nt"></span>
</div></span>
        <span class="nt"><div> <span class="na">class=</span><span class="s">"dt"</span><span class="nt">></span>下拉菜单<span class="nt"></span>
</div></span>
    <span class="nt"></span>
</div></span>
    <span class="nt"></span>
</div></span>  
<span class="nt"></span></span></span></span></code>

要求不高的话用bootstrap 就好了。

做这个功能不难，难的是如何封装和复用。

个人看好polymer这种解决方案。

<code class="language-html"><span class="cp">
<span class="nt"></span>
<span class="nt"></span>
	<span class="nt"><meta> <span class="na">charset=</span><span class="s">"utf-8"</span><span class="nt">></span>
	<span class="nt"><title></title></span>css实现下拉菜单<span class="nt"></span>
	<span class="nt"><style><span class="na">type=</style></span><span class="s">"text/css"</span><span class="nt">></span>
	<span class="o">*</span><span class="p">{</span>
		<span class="k">margin</span><span class="o">:</span> <span class="m">0</span><span class="p">;</span>
		<span class="k">padding</span><span class="o">:</span> <span class="m">0</span><span class="p">;</span>
	<span class="p">}</span>
	<span class="nf">#nav</span><span class="p">{</span>
		<span class="k">background-color</span><span class="o">:</span> <span class="m">#eee</span><span class="p">;</span>
		<span class="k">width</span><span class="o">:</span> <span class="m">300px</span><span class="p">;</span>
		<span class="k">height</span><span class="o">:</span> <span class="m">40px</span><span class="p">;</span>
		<span class="k">margin</span><span class="o">:</span> <span class="m">0</span> <span class="k">auto</span><span class="p">;</span>
	<span class="p">}</span>
	<span class="nt">ul</span><span class="p">{</span>
		<span class="k">list-style</span><span class="o">:</span> <span class="k">none</span><span class="p">;</span>
	<span class="p">}</span>
	<span class="nt">ul</span> <span class="nt">li</span> <span class="p">{</span>
		<span class="k">float</span><span class="o">:</span> <span class="k">left</span><span class="p">;</span>
		<span class="k">line-height</span><span class="o">:</span> <span class="m">40px</span><span class="p">;</span>
		<span class="k">text-align</span><span class="o">:</span> <span class="k">center</span><span class="p">;</span>
	<span class="p">}</span>
	<span class="nt">a</span><span class="p">{</span>
		<span class="k">text-decoration</span><span class="o">:</span> <span class="k">none</span><span class="p">;</span>
		<span class="k">color</span><span class="o">:</span><span class="m">#000</span><span class="p">;</span>
		<span class="k">padding</span><span class="o">:</span> <span class="m">0</span> <span class="m">10px</span><span class="p">;</span>
		<span class="k">display</span><span class="o">:</span> <span class="k">block</span><span class="p">;</span>	
	<span class="p">}</span>
	<span class="nt">a</span><span class="nd">:hover</span><span class="p">{</span>
		<span class="k">color</span><span class="o">:</span> <span class="m">#fff</span><span class="p">;</span>
		<span class="k">background-color</span><span class="o">:</span> <span class="m">#666</span><span class="p">;</span>
	<span class="p">}</span>
	<span class="nt">ul</span> <span class="nt">li</span> <span class="nt">ul</span> <span class="nt">li</span><span class="p">{</span>
		<span class="k">float</span><span class="o">:</span> <span class="k">none</span><span class="p">;</span>
		<span class="k">background-color</span><span class="o">:</span> <span class="m">#eee</span><span class="p">;</span>
		<span class="k">margin-top</span><span class="o">:</span> <span class="m">2px</span><span class="p">;</span>
	<span class="p">}</span>
	<span class="nt">ul</span> <span class="nt">li</span> <span class="nt">ul</span> <span class="p">{</span>
		<span class="k">position</span><span class="o">:</span> <span class="k">absolute</span><span class="p">;</span>
		<span class="k">display</span><span class="o">:</span> <span class="k">none</span><span class="p">;</span>
	<span class="p">}</span>
	<span class="nt">ul</span> <span class="nt">li</span> <span class="nt">ul</span> <span class="nt">li</span> <span class="nt">a</span><span class="nd">:hover</span><span class="p">{</span>
		<span class="k">background-color</span><span class="o">:</span> <span class="m">#06f</span><span class="p">;</span>
	<span class="p">}</span>
	<span class="nt">ul</span> <span class="nt">li</span><span class="nd">:hover</span> <span class="nt">ul</span><span class="p">{</span>
		<span class="k">display</span><span class="o">:</span> <span class="k">block</span><span class="p">;</span>
	<span class="p">}</span>
	<span class="nt"></span>
<span class="nt"></span>
<span class="nt"></span>
<span class="nt"><div> <span class="na">id=</span><span class="s">"nav"</span><span class="nt">></span>
	<span class="nt"><ul></ul></span>
		<span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>按钮1<span class="nt"></span></a></li></span>
		<span class="nt"><li></span>
			<span class="nt"><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>按钮2<span class="nt"></span></a></span>
			<span class="nt"><ul></ul></span>
				<span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>下拉菜单项<span class="nt"></span></a></li></span>
				<span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>下拉菜单项<span class="nt"></span></a></li></span>
			<span class="nt"></span>
		<span class="nt"></span>
		<span class="nt"><li></span>
			<span class="nt"><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>按钮3<span class="nt"></span></a></span>
			<span class="nt"><ul></ul></span>
				<span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>下拉菜单项<span class="nt"></span></a></li></span>
				<span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>下拉菜单项<span class="nt"></span></a></li></span>
				<span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>下拉菜单项<span class="nt"></span></a></li></span>
			<span class="nt"></span>
		<span class="nt"></span>
		<span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>按钮4<span class="nt"></span></a></li></span>
		<span class="nt"><li><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>按钮5<span class="nt"></span></a></li></span>
	<span class="nt"></span>
<span class="nt"></span>
</div></span>
<span class="nt"></span>
<span class="nt"></span>
</span></span></code>

这个是网易云课堂前端微专业的页面布局的期末测试题。 我也试一下。
这里大部分答案都是hover事件触发下拉菜单出现。其实我总觉得这样不太自然，所以我尽力去做成（伪）点击触发。
---------------------------------------------------------------------
# 具体想法：
菜单是， 下拉菜单的容器是

...

然后利用a:focus + .dropdown{ ... } 来实现。
---------------------------------------------------------------------
要点1：CSS如何实现影响其他元素？
看这里 > html - How to affect other elements when a div is hovered
要点2： 如何做出（伪）点击触发？
基本用 a：focus，个人感觉自然一点。当然如果失去焦点，下拉菜单容器也会相应地隐藏。
--------------------------------------------------------------------
# HTML BODY 部分代码：

<code class="language-html"><span class="nt"></span>
     <span class="nt"><a> <span class="na">href=</span><span class="s">"#"</span><span class="nt">></span>Menu<span class="nt"></span></a></span>
	  <span class="nt"><div> <span class="na">class=</span><span class="s">"drop-down"</span> <span class="na">id=</span><span class="s">"drop-down"</span><span class="nt">></span>
		   <span class="nt"><ul></ul></span>
			<span class="nt"><li></span>Option 1<span class="nt"></span>				
                        <span class="nt"><li></span>Option 2<span class="nt"></span>
			<span class="nt"><li></span>Option 3<span class="nt"></span>
			<span class="nt"><li></span>Option 4<span class="nt"></span>
		   <span class="nt"></span>
	  <span class="nt"></span>
</div></span>
<span class="nt"></span>
</code>

更正一点小错误，只有一个单选按钮时，选中后就不能取消选中了。所以最好用复选按钮。

原答案如下
===========================

楼上有同学写了css用伪类:hover实现的下拉菜单 这是一种 我再补充下

下拉菜单抛开样式的不同 交互上无非两种
鼠标移到button上出现菜单（如楼上）
以及点击后出现菜单（我要说的）

题主问的是html+css 而很多同学提到了用js添加click事件 这也是大多数下拉菜单的做法
不过为了不跑题 就只用html+css 不用js 那就考css基本功了

这里简单说下思路

html结构如下

<code class="language-html"><span class="nt"><button></button></span>点击我出现下拉菜单<span class="nt"></span>
<span class="nt"><input> <span class="na">type=</span><span class="s">"checkbok"</span><span class="nt">></span> 
<span class="nt"><div>
	<span class="nt"><ul></ul></span>
		<span class="nt"><li></span>XXX<span class="nt"></span>
		<span class="nt"><li></span>XXX<span class="nt"></span>
		<span class="nt"><li></span>XXX<span class="nt"></span>
		<span class="nt"><li></span>XXX<span class="nt"></span>
	<span class="nt"></span>
<span class="nt"></span>
</div></span>
</span></code>

用列表，隐藏，然后hover.的时候block就可以了 http://pepsized.com/css-only-alternative-to-the-select-element/

如果想用纯css实现click效果:
http://tympanus.net/codrops/2012/12/17/css-click-events/