Fix todo list scrobar background

[PlayXman]

Describe the bug

The background of the scrollbar in todo list is dark even if the overall block has no background. As you can probably imagine this creates unwanted look.

Screenshots

Expected behavior

Make the scrollbar's background transparent.

Desktop (please complete the following information):

• OS: MacOS 11.6.5
• Browser name and version:Firefox 98.0.2
• Plugin version: 3.1.0