Google says images styled with CSS won’t be indexed in Image Search, advising developers to use HTML tags for important ...

images/ ) to that graphic. This is the only property required in order to place an image in the background. Note that, unlike HTML, the CSS code doesn’t use quotation marks in its path to the image.

Using custom CSS, you can add a colored background to your posts without editing your posts in other ways and without changing the background of the rest of your blog's body.