Responsive URL shortening API landing page

I wanna know how you can have a grey background that takes up the whole width in your second section even though when it has width: 75rem. I created a div outside the main and set the position absolute and I just positioned it, but I think it's not a good solution.

Any advice?

Btw this was my first intermediate solution, I'm really mad about the grey background because I think it's scuffed, other than that I'm proud of this.