Use CSS to customize Content Background

I am making a page and on this page I can’t figure out how to use costume css to modify the color of the content background.

I want to use CSS like this: {background-image: linear-gradient(to right top, #3d399b, #005eb5, #007cbd, #0095b8, #00acae, #35b3ab, #51baa8, #68c1a5, #66bda8, #65b8aa, #66b4ab, #68afab);
background-clip: text;
-webkit-background-clip: text;
}

I was able to set it for the body: body {background-image: linear-gradient(to right top, #3d399b, #005eb5, #007cbd, #0095b8, #00acae, #35b3ab, #51baa8, #68c1a5, #66bda8, #65b8aa, #66b4ab, #68afab);
background-clip: text;
-webkit-background-clip: text;
}

But now the body is gradient color while the content background is just white, what is the id that I should use for the content background? Is it possible to make the content background clear all together or remove it so it’s just my columns on top of the page?

I need help for this:
https://user.irngems.com/usergems/?page_id=371