You can also add a background-position attribute to your CSS, with values such as center, left top and right bottom. Add this attribute to make your GIF appear at specific locations in the background.

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

One way to add a background photo to any custom Tumblr theme is to embed a simple CSS tag at the right location in the theme's HTML code.