Comment by silvestrov

I would create new pseudo elements:

    .container:gap { background-color: red; }

This will allow for more fancy backgrounds (e.g. dotted or gradients) and using { padding: 2px } to set whitespace at ends of the seperator.

Possible with a :gap-horz and :gap-vert (or whatever css like to name it) to get seperate vertical and horizontal gaps.

Also: .container:gap:nth-gap(2n) { color: blue; } to get alternating colors.