Hi, Philipp.
That link isn’t accessible to logged-out users so I cannot assist.
Additionally, we do not provide CSS customizations in this free forum or even our paid forum.
A plugin like SiteOrigin CSS may come in handy if you’re not a CSS expert. It helps you visually build CSS selectors via its Inspector and Visual Editor (third-party, not guaranteed or supported by us).
If you need some coding help, you may want to ask your developer or reference our documentation and list of known customizers.
