Slightly darkening the page backcground to f1f1f1 for better contrast with...

Slightly darkening the page backcground to f1f1f1 for better contrast with white interface elements on top of it. See #25858.
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git-svn-id: https://core.svn.wordpress.org/trunk@26724 1a063a9b-81f0-0310-95a4-ce76da25c4cd