Non-empty borders should be respected by theme

[ancwrd1]

If the borders are set to something other than None the theme selection color overlaps the top border. See attached screenshots:

[Zren]

The outline is drawn on top of the hovered rect.

I'm not sure if adding .adjusted(0, 1, 0, 0) to the button's background fill would look much better.

https://github.com/Zren/material-decoration/blob/master/src/Button.cc#L221

[ancwrd1]

I tried it with .adjusted(0, 2, 0, 0) and it does look better I think:

[ancwrd1]

Also reducing one pixel from the bottom makes the menu hovering look slightly better.