弹出层

弹出层即为点击触发时间时，弹出一div

例如：
<a href="#test_title" class='create_test' role="button" data-toggle="modal"
data-backdrop="true" data-show="true">创建试题　</a>//#test_title为div的id

//弹出的div，在其中填写内容
<div id='test_title' class="modal hide fade" aria-hidden="true">
<div class="modal-header">
<a class="close" data-dismiss="modal">×</a>
<h3>创建试题</h3>
</div>
<div class="modal-body"> 
<div style="margin-left:50px;margin-top:20px;margin-bottom:20px">
<font size='3'>试题名称</font>:<input type="text" id="div_title" class="input input-medium" style="font-size:16px"/>
</div>
</div> 
<div class='modal-footer'>
<a href="#" type="button" name='submit' class='btn btn-primary' data-dismiss="modal"/>确认提交</a>
</div>
</div>