This was causing obvious confusion for users - misclicking outside of
the pop-up caused a dismissal where the consequences were not at all
clear.
So let's drop that behaviour entirely. You exit the dialog through
explicit button or key presses only.
- All of our red buttons were ImButton with the colours overridden at the
use site. Instead make an ImButtonRed which defines these colours in
one place.
- Previously the red buttons had focus indicated by the text colour
changing from white to blue. This was quite hard to see, instead
change the button colour to blue (as is done for the white buttons).
A darker shade of blue is used so that there is still good contrast
with the white text.
- Update the reds (buttons and main screen background) with the
branding-approved red: the official colour palette says Pi Red is
#cd2355
