Either get a ply / wood front that can cover between floor and first shelf
That’s a good shout, thanks. I don’t really want to fill under that bottom shelf with a box as I like how the shelves kind of float, but creating a hidden section at the back could work nicely.
Could you make a shallower depth, skirting height box, and front it with the same profile as the skirting, so that you basically have a fake front skirting board 6inches further forward than the wall so it visually diappears, but still does the same thing?
Either get a ply / wood front that can cover between floor and first shelf, or like you say, hide it behind the tv
Or maybe cut the back out of a nice vintage ply / wine box and place it under the bottom shelf