When I do an Inspect on the page it looks like cbOuterAjaxCtnr is where some of the whitespace comes from. When I manually type in a background color (in inspector) it does change the background. However, in the Style Sources if I put the below code it doesn't work and I can't find anything for cbOuterAjaxContainer. This is what I thought it would need:
background-color: #daded1 !important;
Ah, I figured it out if anyone else needs to do the same thing: The background setting needs to not be in a Caspio datapage or Style but in the host web page's css. I guess the datapage uses whatever background css the host page uses for the headers and outer containers.