Radial gradient as background color

Hello. 

I'd like to have a radial-gradient as my background color on the non-banner sections of my index. I've got the gradient code but not sure how to implement the CSS into the site:

body#collection-5dd4869eebd9bd1394120bad .Main {
    background: radial-gradient(ellipse at center, #f2f2f2, #000000);
}

site: https://spinach-viola-en24.squarespace.com/

pass: support

Also, I'm trying to make the gradient look more like the attached image. Is this possible with CSS?

What am I doing wrong?

Thanks for the help.