1925640 - PerfCompare dropdown-menu select widgets have different background-color at the edges, when focused, in dark theme

Status: NEW

(Testing :: PerfCompare, defect)

Description

[Daniel Holbert [:dholbert]]

Attachment: screenshot

STR:

1. Visit https://perf.compare/
2. Click the slider at top-left to enter dark mode.
3. Scroll down to see the Base/Revisions/etc. dropdown-menus
4. Click one of the dropdown menus, and then either choose an option from the menu-popup, or just dismiss the menu by clicking outside of it. (This closes the menu but leaves the widget focused.)

ACTUAL RESULTS:
The middle of the widget gets a slightly brighter color than the left/right edges of the widget (inadvertently revealing the internal parts that the widget is built from, I think).

EXPECTED RESULTS:
Consistent background color across the dropdown-menu-widget.

I can reproduce in Firefox as well as Chrome, so this isn't a Firefox bug.