[UI] button:hover border is hidden when the section has no padding/margin

[elyseviotto]

Describe the current behavior
On hover, the border thickness of buttons change.
When a button is the last element of a section, the border is clipped.


You can see the inconsistency of the button border when the background color is the same for 2 sections.

• You can reproduce and hover your mouse on the button when there's no padding/margin on the section
• See the bug in action: video

Describe the expected behavior
On hover, the border thickness is the same all around the button.

Version information (Dawn, browsers and operating systems)

• Dawn Version: 1.0.0
• Chrome Version 91.0.4472.114
• macOS Version 11.3.1

Possible solution

• The isolate class introduced here might be causing this effect (see video)