formatting widget original theme requires three classes

hi all.

new to wordpress and pretty excited about it so far. i’m modefying Angelina’s SimpsonsHB theme (www.nyceducrats.com) and came upon a formatting problem. the widgets i enter into the site aren’t formatted or styled right.

to match the original themes style it appears i’d need to have three class (one for header, sides, footer) while the widget that gets entered only has one. i could modify the wordpress file (as opposed to the theme) but would like to avoid this in case there are future updates.

CODE OF THEME:

<li class=”side-header”>

<li class=”side-back”>

(content)

<li class=”side-footer”>

THE CSS FOR THEME LOADS THREE IMAGES

.side-header {
height: 6px;
line-height: 6px;
background-image: url(‘images/side-header.gif’);
background-repeat: no-repeat;
margin: 0;
padding: 0;
}

.side-footer {
height: 6px;
background-image: url(‘images/side-footer.gif’);
background-repeat: no-repeat;
margin: 0 0 10px 0;
}

.side-back {
background-image: url(‘images/back-sidebar.gif’);
}

li.side-back ul {
background-image: url(‘images/back-sidebar.gif’);
}

CODE OF WIDGET:

<div class=”widget widget_whatever”>
(content)
</div>

Is there a way to achieve a similar format for the widget from just one class tag?

Any ideas are welcome and help greatly appreciated.