You can use a custom domain instead of
your-project.gitbook.io . See the dedicated page for more info:
Having a logo for your project is the first step to make your reader feel at home. You can add one from the General Settings of your project.
Or from the Logo & Title panel in the customization tab:
The primary color of your project will be used for details in your documentation. Links, for example, use the primary color. It should be the same dominant color used in your logo, or a good complementary color, and it should have enough contrast with white background. Avoid light colors such as yellow. Pick a primary color from the Theme & colors panel in the customization tab.
Header links are typically used to link to your other sites, such as your project's homepage, a forum, or a GitHub repository. You can add them from the Header panel of the Customization tab.