As you know, one of the “weak” points of modern SharePoint Online (SPO) sites is that they cannot be deeply customized using out of the box features. However, Microsoft is starting to provide new customization options to provide some branding to our modern SPO Sites. This options can be found in the Change the look panel that shows us when a site admin or a site owner click on the option with that name:
As you can se, we have the following customization options:
Theme, allows to change current site theme for one of the defaults themes or for a custom theme deployed to SPO.
Header, provides different settings to change the header layout (Standard vs. Compact), the site logo and the header background (you can choose from four different layout options).
Megamenu, it allows to select the navigation user experience in the site. There are two navigation experiences flavours: Megamenu vs. Cascading.
Footer, this setting is itended to set up how the site footer is going to look like in terms of footer logo, footer name or footer links.