Capitals in headers

I managed to solve the problem myself. In the stylesheet (style.css), I changed the line:

text-transform: capitalize;

into:

text-transform: none;

@kebbon Just keep in mind that if you change anything directly in a stylesheet that belongs to a plugin or theme, then your changes will disappear the moment this plugin/theme is updated next time.
CSS you may try to override via Customizer (Anpassaren) – Additonal CSS.

Good point, @tobifjellner – thanks!