As grid offers 12 equally wide columns, you can go 2/3 - 1/3 (e.g.
67/33) with an 8+4 grid, or 58/42 (7+5), which should be visually
reasonably close to not justify coming up with another grid geometry
that would need to implement its own breakpoints for screen width adaptation.
Make your life easy, be 2% off, pick 58/42.
Put that standard grid into a container, and you can even save the
combination with some default content as a separate fragment
