How to mix wood with drywall?

I’m building a built-in cube shelf sized to fit vinyl (12.75 inches tall) and I’m struggling to figure out the best way to blend the drywall sides and back with the wood shelves.

Currently I have 13.25 inches of height on all shelves except the top to account for a drywall ceiling. However, in testing it I realized that 12.5 inches of height vinyl with only .25 inches of clearance would mean you would have to remove and put them in place more carefully, so maybe keeping the top exposed (having more room to work) would be nice, but I still want it to look seamless in the cleats. Any suggestions?

This is also my first time doing any carpentry and drywall work, so any advice/criticism is appreciated.