The above link is not files.gallery, but from our X3 photo.gallery, which is more of a photo gallery website CMS, where you can easily add logo, text and pages.
Files Gallery is supposed to be a clean simple interface, without capabilities of adding your own design elements. I might add some basic customization features in the future. For now, it can be done with some tweaking of the html in `index.php, see this post:
https://forum.files.gallery/d/150-gallery-website-header-and-footer-options-available