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If your theme "blanks out", it is most often an indicator, that one has accidently screwed up a smarty tag (leabing out a curly bracket or the like).
Adding a style defintion to your stylesheet will not do this, unless you've set color:#fff;background:#fff;
Though, make sure you close all style definitions with the closing curly bracket (in the code you pasted, the closing curly bracket is missing). If you drop curly brackets, the following styles will be ignored.