Make WordVault tiles a bit more readable

[domino14]

Here are some screenshots of WordVault and WordWalls on a phone.
Maybe it's a combination of the letter size / tile spacing / contrast but it seems to me that the WordVault card is harder to read. Could we experiment with some of these parameters a bit?

The WordWalls tiles are purposely oversized (letter to tile ratio), we probably don't need to go that high to make WordVault more readable. Let me know what you think. @BenMusch

[BenMusch]

@domino14 Yeah I agree here -- studied a bit on mobile while walking the dog and I think a higher front-to-tile ratio is best. Not all that different from the scrabble tiles designed for people with impaired vision

[domino14]

Check this out #485 -- we can iterate on this later if you want. I think making those letters bigger on mobile fixed a lot of the problem.