鼠标移上去显示内容

<style type="text/css">
a {
    position: relative;
}

a div {
    display: none;
    color: red;
    width: 200px;
    height: 200px;
    background-color: #FF0;
    position: absolute;
    top: 20px;
    left: 20px;
    cursor: default;
}

a:hover div {
    display: block;
}
</style>
<a href="#">
    aaa
    <div>aaaa</div>
</a>