Centering a div using CSS align-items & justify-contents

What are you most proud of, and what would you do differently next time?

What I'm most proud of here is the time. The project has been finished like 10 min. I'm not at starting level. I've been coding for 2 years. Due to the fact that the outlines of coding languages are alike each other the learning part was not very difficult. But the centering the div was the hardest part ever. I'll definitely don't try to center the div with px's or %

What challenges did you encounter, and how did you overcome them?

As I said, the centering part was quite interesting and hard. After I researched a bit about how to center a div, I found an information. It was about using the align-items, justify-contents etc.

What specific areas of your project would you like help with?

For now, I don't really need an help. But I'm sure that the other problems'll not be like that easy.