Dear Peter @peti-peti
Yeah sure :)
You would target the highest parent of the heirachy and all its descendants will inherit that CSS :)
Things like 'site title' and a solid 'navbar' you can turn off in 'Customise' in the Wordpress admin bar (left bar)
You may also have a 'padding-top' that you can change within Laytheme's Options'
So we would target the specific page like you have done:
.slug-startseiteThen i believe you want the highest parent which would be 'laynav' but also on mobile a Burger menu would appear so:
.slug-startseite .laynav, .burger-wrap { display:none; }Let me know how that goes for you Peter, or if i answered your question correctly and have a wonderful day :)
Best
Richard