If all you want is to add extra links to the top navigation bar, or extra tabs to the repository view, you can put them in `extra_links.tmpl` and `extra_tabs.tmpl` inside your `custom/templates/custom/` directory.
For instance, let's say you are in Germany and must add the famously legally-required "Impressum"/about page, listing who is responsible for the site's content:
just place it under your "custom/public/" directory (for instance `custom/public/impressum.html`) and put a link to it in `custom/templates/custom/extra_links.tmpl`.
To match the current style, the link should have the class name "item", and you can use `{{AppSubUrl}}` to get the base URL:
Google Analytics, Matomo (previously Piwik), and other analytics services can be added to Gitea. To add the tracking code, refer to the `Other additions to the page` section of this document, and add the JavaScript to the `custom/templates/custom/header.tmpl` file.
As of version 1.6.0 Gitea has built-in themes. The two built-in themes are, the default theme `gitea`, and a dark theme `arc-green`. To change the look of your Gitea install change the value of `DEFAULT_THEME` in the [ui](https://docs.gitea.io/en-us/config-cheat-sheet/#ui-ui) section of `app.ini` to another one of the available options.