I have a menu which consists of items linking to "standard" pages (like Homepage or Contact form) but also to some which have a redirection to some element via anchor (or #link).

When you click to Homepage or Contact form link, there is visible the page and menu item is underscored.
But when you click to page with redirection to some anchor on page (via #link) and page is scrolling to that anchor, the underscore still stays on e.g. Homepage.

How to achieve that effect?

Maybe some details behind - I add that anchor in particle details in the field CSS ID (on Block tab), then I open the page and fill in the anchor into the redirect field of that page which is associated with menu item.

Is there any possibility how to also "setup" the underscore?

You can see that on page www.preloz.to (suddenly in Czech language), but the first one is Homepage (Úvod) and the second one "Překlady" which is not working. The same situation with items "Ceník" and "Kontakt". But "Poptávka" is working.

Is there some solution to that issue?