Changing the text style in the HTML is possible thanks to Cascading Style Sheets (CSS), the stylesheet language used to describe the presentation of a document in HTML.

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.

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.