Remove background for pics onl in sidebar

All my pics in my blog have a shadow i edited in style.css.

a:active img {
border:none;
background:none;
padding:none;
background:url(img/shadow.gif) no-repeat right bottom;
padding:4px 10px 10px 4px;
border-top:#eee 1px solid;
border-left:#eee 1px solid;
}

i have allso pics in my sidebar. How can i remove the shadow from there?