They've cleverly shied away from specifics 🤣 near as we can tell, Gems have some form on DNA (though that's only Word of God from one of the Q&A sessions) or at least have the ability to create something compatible with human DNA. Greg and Rose conceived and, just before he was born, Rose 'poofed' herself and passed her gem to Steven. Presumably in the process (as Gems are also a kind of AI thing) wiping out most of her memories and personality: literally becoming the other half of the blank-slate that is Baby Steven.
But yeah, it's all hints and some Q&A off-the-cuff responses so it's not really concrete.
Vinhthta wrote: Any chances that Pink Steven have Pink Diamond's memories?
Seems like he has 'ghosts' or afterimages of them. A bit like when you erase magnetic storage (like a spinning-platter hard disk, or VHS/audiotape) - you can still pick up a very faint image of what was there before. Least that's how I read into it 🙂