Context menu scrollable arrows incorrectly sized

[hanaral]

What Happened

The newly added scrollable indicator arrows in context menus take up more space than they (look like) should:

https://user-images.githubusercontent.com/58219504/104836779-488ecc00-58a8-11eb-8ff3-3e41b9bf16cb.mp4

Expected Behavior

The arrow's backdrop ends at where the dark line is drawn

Platform Information

elementary OS 6 Daily

[pongloongyeat]

Seems related to elementary/applications-menu#423