The best way to sort out these kinds of issues is by using a browser tool such as Firebug — it shows you exactly what CSS code is affecting an element on the page and helps you see what CSS selectors you need to use to modify or add styles for a particular element.
It’s also highly recommended that you use a custom CSS option if your theme has it, or a plug-in or a Child Theme for making changes to the theme.
Thanks! As only an occasional builder of websites, I often need a refresher when doing things. Firebug is great, and I found the CSS I was looking for and successfully modified it with a Child Theme. Looks just as I’d hoped now.
In case anyone else is digging through their CSS unsuccessfully, I modified .widget-area.