Scrollbar always appears in sounds tab and costumes tab

[BoomerScratch]

Related to #2295

Expected Behavior

Scrollbars do not appear in the sounds and costumes/backdrops tabs. (If there are not many costumes/sounds)

Actual Behavior

They do.

Steps to Reproduce

Open a project and switch to the sounds/costumes/backdrops tab.

Operating System and Browser

Chrome 83.0.4103.116, Windows NT 10.0.

[BryceLTaylor]

This is a browser level setting that we don't control but account for in our design.

[fsih]

@BryceLTaylor I think we could remove those scrollbars if we wanted to. They don't appear by default on Macs, but they aren't forced to appear on Windows

[BryceLTaylor]

@fsih They appear to me on mac. It's a browser setting. (possibly an OS level setting). Discussing with @carljbowman, we decided that this behavior is acceptable.

[BoomerScratch]

@BryceLTaylor @fsih This is easily fixable: the problem is overflow-y: scroll, which should be overflow-y: auto.
https://github.com/LLK/scratch-gui/blob/81664880021571a9144691379b584305f3b5e703/src/components/asset-panel/selector.css#L50
But if you want to keep it like it is, it's okay.