With CSS Grid math you can fake it, at least. If your DL is `display: grid;` and if you have a few extra DIVs lying around at the bottom of the DL to be borders

With CSS Grid math you can fake it, at least. If your DL is `display: grid;` and if you have a few extra DIVs lying around at the bottom of the DL to be borders around combined cells you just have to math which rows/columns you want to draw a border around and make the div fit that combined shape.