How do I get my author avatars list plugin widget to display multiple columns when it is set to disp

I'm using the author avatars list plugin by P. Bearne. It displays my authors in a grid via a widget. It has multiple fine grain settings. (Does WPMU Dev have a similar plugin?) Among other things, it allows to me to choose whether to display the avatars with or without the author names. I would like to display the avatars with the user names. However, when I do so, they change to a single vertical column. When I go into firebug to detect which css rule is causing this, it indicates that widget.css line 12:
.multiwidget_author_avatars .author-list .with-name {
display: block;

If I eliminate this rule in firebug, they change back to the multi-column display I like. However, when I modify widget.css in the real world, it has no effect. How can I get the multi-column / rows with user names displayed? (I'd like to send you the URL to my site so you can see it but I don't want to publicly display the URL here. How can I get it to you?)