FIXED: Problem with responsive grid layout

UPDATE: Fixed, it was a margins issue and I realized it needs to be fixed so I wont even have it as a grid item anymore.

Summary

Hi everyone!
I have one last test to pass on my documentation page, but unfortunately this is my first time using grid, I’m used to using flexbox but I wanted to try it out here, and I’m a bit confused.
Here’s my pen:
https://codepen.io/virginiab/pen/dKXyKB
As you can see, the left column should be filled up by the navbar, which is instead leaving margins all around.
Why does this happen and how can I fix it?