Create a GRUB theme according to the mockup and these specifications:

https://share.kde.org/index.php/s/CUJB96B7daE0buh

The grub menu has to be minimalistic in format. The criticism towards the old
grub menu was that the blue color was too sharp and sudden. It also caused
issues with the "dark square" that turn up after grub menu and the issues with
the sudden sharp break between the blue grub menu and scrolling text when
Plymouth doesn't work (due to proprietary drivers).

In this redesign we have essentially taken the earlier proposed grub menu
design but changed the background to black and having the highlight be the
object in bold and white (#ffffff) instead of the standard, normal font weight
and light grey (#eff0f1)