Thanks for your reply. I’m fairly certain it isn’t a cache issue, as I’ve been emptying my cache and refreshing as well as checking in multiple browsers. Editing the plugin’s stylesheet was a decision of necessity: I also tried changes to my theme’s main stylesheet, but these weren’t doing anything (I was even trying them using the Web Developer plugin to see the changes in real time, and nothing was happening using the same markup that does temporarily work if I put it in the plugin’s stylesheets).
The really strange thing is that what’s worked–making changes just in the plugin’s CSS–stops working after a few days. The changes are still there if I look in the CSS file, but they just cease to have any effect on display.