Hi there,
Try this CSS:
body.page-id-47, .page-id-47 .site-header, .page-id-47.separate-containers .inside-article, .page-id-47 .site-info {
background-color: #333;
}
You can use the disable element to hide the default menu:
https://docs.generatepress.com/article/disable-elements-overview/
If you need to hide the menu globally, you can use the customizer option:
https://docs.generatepress.com/article/navigation-location/
Let me know if this helps 🙂