为什么菜单下拉隐藏在jQuery按钮后面?
div.menu ul li a, div.menu ul li a:visited
{
background-color: #465c71;
border: 1px #4e667d solid;
color: #dde4ec;
display: block;
line-height: 1.35em;
padding: 4px 20px;
text-decoration: none;
white-space: nowrap;
position: relative;
z-index: 9999;
}