We want to be able to express opaque grids. This means that the app
provides either a row of columns of opaque nodes or a column of rows,
and then the containers will magically figure it out.
The main use case for this is terminals, which are uilt using cells. And
when there's a transparent background configured but the contents are
opaque, it'd be nice if we could figure that out.
Also remove the 80% requirement. It is rather arbitrary and while it
helps for some cases, the aforementioned grid would suffer.
