Background color not changing (even after waiting and clearing cache)

Hello all!

I am working on a client site and I am trying to style an unauthorized message page so that the background is all white instead of gray. A few weeks ago I successfully styled this page:

https://maddymoon.com/freedomlounge/members/

simply by adding in the following CSS:

.page-id-9147.page-template-default .site-inner {
background: #fff;
}

Now I want to add this CSS to change the other two unauthorized page messages:
https://maddymoon.com/freedomlounge/month-1-tfl/
https://maddymoon.com/freedomlounge/month-2-tfl/

I added the same CSS with the correct page id in the inspector tool, and I see the background change on these pages when I do it live. When I add the code into the actual CSS, the changes don’t occur, even after waiting 3 days. I cleared the cache using the W3 cache plugin several times and still nothing. I also have updated both WordPress and the genesis parent theme. Plugins all up to date as well.

Ideally, since these are all child pages of a specific page, I want to just add one piece of code that changes all the backgrounds white in these specific child pages:

.page-child.parent-pageid-8983 .site-inner {
background: white;
}

This above code also works when I make the changes live with the inspector tool, but the changes do not show when I update the actual CSS.

Any help is greatly appreciated!