菜鸟求助!!!!!
<style>body{ font-size:12px;}
#top{position:absolute;}
#top a img{-moz-opacity:0.5; filter:alpha(opacity=50);border:0px;}
#top a:hover{font-size:9px;}
#top a:hover img{-moz-opacity:0.5; filter:alpha(opacity=80);cursor:hand;}
</style>
这里面的top是起的什么作用????
还有这个a,a:hover是什么用的?????
