@veleno: There is no space in between, it’s just an optical thing. If you want to remove the optical space, edit (or create) ~/.config/gtk-3.0/gtk.css
and insert:
sq_view sq_button {
border-radius: 0px;
margin: 0px;
}
To remove the optical space entirely. Higher values (in pixel) create optical space and rounded border edges.
You need to restart Phosh to apply the change. So open Terminal and write sudo systemctl restart phosh
or just restart your phone. No recompiling required.
But if you just want to add another button left or right: you need to do some math. The buttons will keep their ratio and scale together to the largest amount of space in X or Y direction. So if one dimension is not perfectly calculated, you will see empty bars on X or Y direction. To make it easier, I share the ratio data I was using for my layouts.
100% and 200% screen scale: 360 x 210 pixel
125% screen scale: 576 x 210 pixel
150% screen scale: 480 x 210 pixel
175% screen scale: 411 x 210 pixel
Your screenshot shows 206 pixel height, so you may want to increase the common button to 45px height before you change your width size. You can add as many button as you want, as long as the width is together not larger than these numbers here.