Because Tumblr themes are nothing more than text files that contain HTML, you can copy your theme and save it on your computer. Performing this task is an excellent way to back up your theme before editing it.

Copy Your Code

Navigate to your Tumblr Dashboard page and click the settings icon, which is shaped like a gear. Click the name of the blog whose theme you'd like to copy, then "Customize" and then "HTML." Tumblr displays your blog's HTML code in an editor. Click inside the editor, press "Ctrl-A" and then "Ctrl-C" to copy all of the code to the Windows clipboard.

Save Your Code

Open a new Notepad document, click anywhere inside it, and press "Ctrl-V" to paste the code you copied from Tumblr. You can save it using any name you like, but a good descriptive name will help you identify the code later. If you ever want to restore your Tumblr template to its original state, return to the HTML editor and delete the code that's in it by clicking inside the Editor and pressing "Delete" or "Backspace." You can then copy the code that you saved in your Notepad document and paste it into the HTML editor.