Can't Center Divs

You've tried every flexbox and CSS Grid property known to humanity, consulted three different Stack Overflow threads, sacrificed a rubber duck to the coding gods, and yet that div sits there like a stubborn toddler refusing to move to the middle of the screen. The SpongeBob image of Squidward lying in bed, exhausted and defeated, captures that exact moment when you realize you've thrown literally every centering technique at the problem and it's STILL not centered. Maybe the div just enjoys watching you suffer. Pro tip: Did you remember to set the parent container's height? No? There's your problem. You're welcome.