Nested frames wont fix to cols

I have two frames which will fix width to cols when not framed together.

I want to frame the two child frames together so they scale with each other i.e. share the fill of the container), however when I frame them, the the original fix to col stops working.

Think of a persistent drawer and body with beside it. When the drawer disappears i want the body frame to fill that space and when the drawer is present, i want it to shrink to let it exist on the screen.

Do you need something like this?

Similar as long as resizing the highest level parent frame scales the side panel and the main content fixed to cols?