Adding grey background section

Hey,

I want to make my background just like the one found at https://www.gluestore.com.au/
That is, I would like the top 2/3 of my background white and the bottom 1/3 grey.

I know i need to adjust the container code in my style.css, but I cant figure this out.
Any help would be much appreciated!

My site is https://zegare.com