Hundreds of custom free and proprietary Tumblr themes are available to give your blog a whole new look and feel. If you are proficient with HTML and CSS, you can also create your own custom themes for the platform. When you apply a custom theme to your blog, the theme changes the way you modify your blog’s appearance. To change your background image in a custom theme, you must directly edit the theme’s CSS code in the HTML page. The new image must be also accessible via a URL and must be in a Tumblr-compatible format.

Step 1

Open Tumblr and log in to your dashboard. Click the name of the blog to modify in the right panel, then click the “Customize” link under the selected blog’s name. The blog opens with the Customize tool added to the left side of the window.

Step 2

Click the “Edit HTML” link to open the HTML editor.

Step 3

Press “Ctrl-F,” then type “body {“ in the Find box to find the “body” tag. Locate the “{background-image” tag in the body section, then find the “url” attribute for the image tag.

Step 4

Replace the existing background image URL in the “url” attribute of the image tag with the URL to the new image.

Step 5

Click the “Update Preview” button to view the changes in the Preview panel, then click “Save” to save the theme.