鼠标悬停，会变亮的CSS按钮

<title>变亮效果的CSS按钮</title>
<style type="text/css">
.aaa {
    height: 22px;
    width: 72px;
    background-image: url(http://www.codefans.net/jscss/demoimg/201105/chakan_btn_bg.gif);
    font-size: 12px;
    line-height: 22px;
    text-align: center;
    display: block;
    text-decoration: none;
    background-repeat: no-repeat;
    background-position: 0px 0px;
}
.aaa a:link {
    height: 22px;
    width: 72px;
    background-image: url(http://www.codefans.net/jscss/demoimg/201105/chakan_btn_bg.gif);
    font-size: 12px;
    line-height: 22px;
    text-align: center;
    display: block;
    text-decoration: none;
    background-repeat: no-repeat;
    background-position: 0px 0px;
}
.aaa a:hover {
    height: 22px;
    width: 72px;
    font-size: 12px;
    line-height: 22px;
    text-align: center;
    background-image: url(http://www.codefans.net/jscss/demoimg/201105/chakan_btn_bg.gif);
    background-position: 0px -22px;
    display: block;
    background-repeat: no-repeat;
}
</style>