Stand alone OR Popup styling

I installed WP-Email on my site and I have really enjoyed this plugin! The one issue I have is that when click on Email This Page, whether I use the Popup or the standalone page, the resulting background takes on the background of the page I was on. Usually that would be pretty logical but in this case, the background image the client is using just doesn’t work well with the email form.

So, how I can change that background, perhaps to something as simple as a white background? If it involved CSS could you please give me a push in the right direction there? I’m quite the novice with CSS