Border colors don't get set correctly when widget is in focus if not specified

[jwlodek]

Describe the bug
When the focus border color is not explicitly set, it defaults to widget color, instead of border color.

To Reproduce
Steps to reproduce the behavior:

1. Set widget border color to non default value
2. Select widget

Expected behavior
Focus border color should retain standard border color if not directly specified

Screenshots
In the below image the warning popup is broken since the focus border color defaults to WHITE_ON_BLACK despite the border color being set to YELLOW_ON_BLACK

Environment:

• OS: N/A
• Terminal: N/A
• Version: v0.1.2