Grid container height doesn't fit all of its children

I'm trying to create a bracket in html and I ran into an issue where my original container doesn't seem to fit all of its children, it's just barely too small. As you can see on the screenshot the container's height ends and its padding (that I added there to make it not cut off the last item) starts. Any idea what makes the container too small? I noticed that if I remove my <h3>s at the top of every column then the container's height is correct and padding isn't needed, not sure if it's related. Here's the link to a tailwind playground, sorry if it's messy: https://play.tailwindcss.com/REG3wRZEwt

Tailwind Play

Tailwind Play

An advanced online playground for Tailwind CSS that lets you use all of Tailwind's build-time features directly in the browser.