.byuser class for authorcomments??? problem?

hi there,
i simply want to make all .byuser comments on my blog in a different color. since wp 2.7 the style.css has a
ol.commentlist li.byuser {} class to style the author and byuser comments.

however, i’m using the modicus-remix theme and unfortunately the comments aren’t built with a list-element.

in this theme the comments are a loop of a div-element with the class “bubble”.

div.bubble {
    margin-bottom:24px;
    width:auto;
}
/* i tried to add the div.byuser class -> doesn't work -> all divs with the bubble class get colorized!!! ??? */
div.bubble, div.byuser{
    background-color:#CCCCFF;
}
div.bubble blockquote {
    border:1px solid #C9C2C1;
    margin:0px;
    padding:10px;
    background:#fff;
}
div.bubble blockquote p {
    line-height:1.3em;
    margin:0px;
    padding:0px;
}
div.bubble cite {
    background:transparent url(images/tip.gif) no-repeat scroll 20px 0pt;
    display:block;
    font-size:1em;
    font-style:normal;
    margin:-7px;
    padding:7px 0px 10px 15px;
    position:relative;
    top:5px;
}

is there a chance to style this div.bubble element if it comes from an author? or does this .byuser class only work with list-elements.

as you can see in my sample css i tried to add this few lines, however it doesn’t work:

/* i tried to add the div.byuser class -> doesn't work -> all divs with the bubble class get colorized!!! ??? */
div.bubble, div.byuser{
    background-color:#CCCCFF;
}

??? any ideas ???