There is a bit of a bug in that exercise.
First, move your comment below your style element, you want that style element to start on the very first line.
If that doesn't work, give this a try.
5/21 - Firefox gives Oops! try again with no other details.
Workaround 1: use a different browser.
Workaround 2: remove all of your code and leave only the style tags. You will need to replace your code on the next lesson.