css: list-style-image で画像の背景を設定するにはどうすればよいですか?

/*-----------------------------------.top10-----------------------------------*/
#top10 li {
        line-height:160%;
        padding-left:24px;
        border-bottom:1px #ccc dashed;
        width:150px;
        overflow:hidden;
}
#top10 a:hover {
    color:#C90;
}
#top10 .top1 {
        background:url(images/top_1.gif) no-repeat left center;
}
#top10 .top1 a {
    color:#06f;
}
#top10 .top1 a:hover {
    color:#f60;
}
#top10 .top2 {
        background:url(images/top_2.gif) no-repeat left center;
}
#top10 .top2 a {
    color:#06f;
}
#top10 .top2 a:hover {
    color:#f60;
}
#top10 .top3 {
    background:url(images/top_3.gif) no-repeat left center;
}
#top10 .top3 a {
    color:#0066FF;
}
#top10 .top3 a:hover {
    color:#f60;
}
#top10 .top4 {
    background:url(images/top_4.gif) no-repeat left center;
}
#top10 .top5 {
    background:url(images/top_5.gif) no-repeat left center;
}
#top10 .top6 {
    background:url(images/top_6.gif) no-repeat left center;
}
#top10 .top7 {
    background:url(images/top_7.gif) no-repeat left center;
}
#top10 .top8 {
    background:url(images/top_8.gif) no-repeat left center;
}
#top10 .top9 {
    background:url(images/top_9.gif) no-repeat left center;
}
#top10 .top10 {
    background:url(images/top_10.gif) no-repeat left center;
}