Just curious, was it necessary to switch anything around or we could just leave it the way it is?
I'm not sure what you mean? Of course you don't have to switch things around; if you don't, you'll have the CSS ordered the way I chose, which I think is pretty great. If you want it ordered like in standard Project M, you can switch it around - but I think keeping an order designed for one layout of rows and columns and applying it to a different layout is a terrible idea (and I wasn't a fan of Project M's order even on their layout).
I've been thinking I should explain the reasoning behind my ordering, so I'll go ahead and do that. There's a lot that I'm really happy with and don't want to change, but there are also some decisions that I'm much less sure about.
A few main obvious things - every franchise is grouped together horizontally (and DK, Yoshi, and Wario are with the Mario franchise); the franchises represented by only a single character are all together on the bottom row; and unless there's a reason to do things differently, the order is chronological.
Obviously it starts with Mario, and his group of 8 characters. Within the Mario franchise proper, chronologically it's Mario, then Luigi, then Bowser/Peach (both introduced in the same game). I put Peach before Bowser - this matches Brawl and Project M, but Melee did it the other way around. I don't have a strong opinion on this, and could switch if there's a reason.
For the Mario-related franchises, chronological order would be Donkey Kong, then Yoshi, then Wario. I put Yoshi first because I feel he's even more of a Mario character than the others. Looking at it again now, I think I may move Wario in front of Donkey Kong as well - I don't really like having just the one after Donkey Kong's two, and he feels more tied to the Mario franchise now that he's in his overalls. And Diddy Kong is pretty clearly the least tied to Mario of the 8, so him being last feels right.
After the Mario group there's three more slots on the first row - I could have put Fire Emblem there, as the oldest of the franchises with three characters, but I thought Kirby worked better - more similar to Mario and more important than Fire Emblem. I put Meta Knight after King Dedede (unlike Brawl and Project M) because he didn't appear in the first Kirby game, so he's later chronologically, and I didn't see a reason to switch that up. (Not sure why Brawl did.)
To start the next row we have the next franchise chronologically, the Legend of Zelda. I went with chronologically ordering - Link and Zelda from the original, Sheik and Ganondorf from Ocarina of Time, then Toon Link from Wind Waker. The obvious potential change is moving Toon Link next to Link - would people like to see that?
After that there are six more slots on the row, which go to the two franchises with three each remaining, Fire Emblem and Star Fox. Fire Emblem is first because chronology, and is Marth, Roy, Ike because chronology. Star Fox is Fox, Falco, Wolf, because of course.
Third row has Metroid, Mother, and Pokemon, in that order because of chonology, again. Metroid and Mother's ordering is again obvious and straightforward.
Pokemon has 6 from generation one, and Lucario. So obviously I put Lucario last. I put Mewtwo next to Lucario. I started with Pikachu then Jigglypuff, because of them being in the first Smash. The Pokemon Trainer pokemon were ordered with the lowest evolution first. I'd be open to potentially reordering these if there's a reason, but I'm pretty happy with this order.
For the final row, it's again chronological order (of the Nintendo characters), with the exception of R.O.B being moved before the Ice Climbers in order to be next to Mr. Game & Watch. Then it's the guest characters, in chronological order, then Random.
One potential change would be moving Random to the middle of the bottom row, instead of the end. Separating the 4 retro characters from the others. Not sure what I think about that - anyone else have an opinion?