Stopping your Tumblr sidebar from scrolling requires a small edit to your blog theme's HTML code. Because every Tumblr theme is different, the steps for making this change vary from one theme to another. Although it may take a little trial and error, you should be able to make the change yourself without any advanced knowledge of HTML coding.

Step 1

Click "Customize" on your dashboard, and then click "Edit HTML" on the Customize page to view your theme's HTML coding.

Step 2

Press "Ctrl-F" to bring up the search tool, and then enter "<style" (without the quotes) into the search field. The cursor jumps to the beginning of the cascading style sheet section, which begins with the tag "<style type="text/css">".

Step 3

Scroll through the code until you find a line that begins with something similar to ".sidebar" or "#sidebar". In some cases, assuming the sidebar is on the right, the line may begin with something like ".right_col" or "#right-column". If you can't find the right line, or you're not sure, use the trial-and-error method later in the steps.

Step 4

Find the declaration "position: relative;" that comes after the "{", and change it to "position: fixed;".

Step 5

Click "Update Preview," and then scroll your blog in the preview pane to see if your change worked. If the sidebar stopped scrolling, you're done; click "Save" and exit the Customize screen. If the sidebar still scrolls, then you changed the wrong code; undo the changes and continue with the next step to use the trial-and-error method.

Step 6

Enter "position:" (without quotes) into the search field and find the next line that contains the search text. Replace "'relative" with "fixed." Click "Update Preview," and then scroll your blog in the preview pane the see if the change has the desired effect. Repeat this step until you change the right line of code, making sure you undo your changes after each wrong try.

Step 7

Click "Save" after you change the right line of code.