Then I cut a piece of particle board we had lying around from our floor redo (which I haven't posted on here because I don't have any good after photos of the floor yet) and screwed it on top.
Now my platform is even less attractive than it was previously because the two types of plywood don't match. So I bought some contact paper and covered the whole thing with zig zags!
It did get a little ripped when the appliance installers put the machines in, but I had enough contact paper to just cover up the tears. It doesn't look excellent, but it does look better than that awful particle board! And really, who's looking at the base with those beautiful big machines sitting on top? I never thought I would be so excited by appliances!