Hiding Footer Doesn't Hide Background Color

Site URL: https://www.ncbcenter.org/matching-gift-august-2020

Somewhat urgent request: I'm trying to create a custom blank page to use for a complex landing page we need to build, and I need to hide the site header and footer.

https://www.ncbcenter.org/matching-gift-august-2020

The site uses Mojave, 7.0.

I've inserted this code into the Custom CSS for the page collection ID, but it still keeps showing the background color for the footer (although the other footer elements are hidden).

#collection-5f33fb833ef2451f22c501d0 {
  header, footer, .Mobile-bar--top {
    display: none!important;
  }

How do I hide the background color as well, please? Thank you!