I'm using a Twitter plugin on a WordPress site. I need to change the title (Twitter: name) to a background image and style a shaded margin around each twitter item - so there is a grey bordered frame with each tweet in a white square inside and a header graphic at the top. Since I have no control over the HTML I'm having trouble writing the CSS selectors that will make these changes. This is the markup of the plugin from view source of the page:

<aside id="twitter-4" class="widget widget_twitter">
  <h3 class="widget-title"><span class='twitterwidget twitterwidget-title'>Twitter: name</span></h3>
    <li><span class='entry-content'>first twitter post</span></li>
    <li><span class='entry-content'>second twitter post</span></li>
I've tried adding a background image to all the various classes before the name but none of them work. The same with the grey margin.

The problem with trying to style stuff in WordPress plugins is it's hard to tell which selector you need to override the plugin CSS and what else is in the cascade that you can't see that's preventing it from working.