The best fix possible atm is having them be more "square-ish" but they stay pretty small.
Making them wider breaks the color pickers since these 2 elements are linked without a way to assign different sizes to them without modifying the source code of aseprite so atm this is the best solution until they add a way to change this inside the theme files ):
I'll post these changes in the next update but sadly this will have to be a compromise for the theme atm