Widgets: Highlight color of selected sidebar is blue in each color scheme

[ocean90]

Same for widgets in the Customizer.

[nacin]

It looks like the patch also removed some border accents for the widget area chooser that isn't present on the present-day widgets screen. (Maybe it was at one point and these diverged, I'm not sure.) It all looks good to me.

[ocean90]

Replying to nacin:

It looks like the patch also removed some border accents for the widget area chooser that isn't present on the present-day widgets screen.

That's true. There are no borders on the widgets screen, so I have removed them here too. You can see the difference in 27793.customize-before.png​ and 27793.customize-after2.png​.

[nacin]

In 28122:

Color scheme support for widget choosers.

props ocean90.
fixes #27793.