desktop如何设置桌面图标

我在EXT的demo上照着例子加了两个桌面图标 但是不显示图标 只显示图标下面的文字 请问在哪设置这个图标啊

desktop.html
[code="html"]




Grid Window




Accordion Window


[/code]

样式在\css\desktop.css

[code="html"]/* shortcuts */
#grid-win-shortcut img {
width:48px;
height:48px;
background-image: url(../images/grid48x48.png);
filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(src='images/grid48x48.png', sizingMethod='scale');
}
#acc-win-shortcut img {
width:48px;
height:48px;
background-image: url(../images/im48x48.png);
filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(src='images/im48x48.png', sizingMethod='scale');
}[/code]