用css写出一个小三角形图标

<div class="box">
<div class="list_a">
<ul>
<li><em></em>24h短讯 </li>
<li><em></em>24h短讯 </li>
<li><em></em>24h短讯 </li>
<li><em></em>24h短讯 </li>
<li><em></em>24h短讯 </li>
</ul>
</div>

.list_a{ width:200px; height:auto; margin:20px auto;}.list_a li { height:25px}.list_a em { display:block; border:4px solid; border-color:#fff #fff #fff #ff0; float:left; margin-top:7px}

css写出滑动条的样式.yixianCon{overflow-y:auto;overflow-x:hidden;width:410px;height:400px; padding-left:5px;}.yixianCon dl{border-bottom:1px solid #ebebeb;padding-bottom:10px;font-size:14px;margin-top:5px;line-height:170%;}.yixianCon dt a{font-size:14px;padding-left:5px;width:360px; display:inline-block;}.yixianCon dd a{font-size:14px;color:#999; line-height:20px; padding-left:15px;}.tro a{color:#999;}.yixianCon em { display:block;  border:4px solid; border-color:#fff #fff #fff #F00; float:left; margin-top:7px;}.con dd{font-size:14px;color:#999; line-height:20px; padding-left:15px;}.con dt span{font-size:14px;padding-left:5px;width:370px; display:inline-block;}