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.

How do you change a web sites .css client-side? What do I do with the above code? I've been out of the hard-core web design stuff for too long, but I really would like the black background back.

John said this also back in January 2018 when he said Google Image search does not index and rank images from CSS background code.

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.