bootstrap弹出框与背景都是灰色

  <div class="navbar navbar-inverse  navbar-fixed-top">
                <div class="navbar-inner">
                  <div class="container">   
               <div class="nav-collapse collapse">
              <ul class="nav">
               <li class="">
                  <a href="#myModal" data-toggle="modal">注册</a>
                </li>

                <li class="">
                  <a href="#myModal" role="button" class="" data-toggle="modal">登陆</a>
                </li>
              </ul>        
                </div>

                <!-- Modal -->
<div id="myModal" class="modal hide fade" tabindex="-1" role="dialog" aria-labelledby="myModalLabel" aria-hidden="false">
  <div class="modal-header">
    <button type="button" class="close" data-dismiss="modal" aria-hidden="true"></button>
    <h3 id="myModalLabel">Modal header</h3>
  </div>
  <div class="modal-body">
    <p>One fine body…</p>
  </div>
  <div class="modal-footer">
    <button class="btn" data-dismiss="modal" aria-hidden="true">关闭</button>
    <button class="btn btn-primary">Save changes</button>
  </div>
</div>
            </div>
        </div>

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有id呢，自己这个样式覆盖下不行吗？