Hello,
Please check my first reply > Private Content area, you will find screenshots of how your site is displayed for me. You need to clear cache of your browser, because all changes are visible (background color and Style), when there is no cached version – https://prnt.sc/N8Q4jkLr_kuk
https://support.google.com/accounts/answer/32050?hl=en&co=GENIE.Platform%3DDesktop
Color of custom headings can be changed via settings of elements, for example, https://prnt.sc/zkPSVqsgJV4X
Regards