1.     <div class="box1">
    2.         <a href="javascript:;">这是一个超链接</a>
    3.         <div class="box2">这是下拉菜单</div>
    4.     </div>
    .box1{
    width: 100px;
    height: 40px;
    background-color: #ff0;
}
.box a{
    display: block;
    height: 40px;
    width: 100px;
    line-height: 40px;
    text-align: center;

}
.box2{
    width: 500px;
    height: 200px;
    background-color: teal;
    display: none;
    position:absolute;
}
.box1:hover .box2{
    display: block;
}