Thank you for your quick reply!. I tried that just now, but the result stays the same. The general selector I used initially, #jmap_sitemap, gives the same result. The color change and the sans-serif part both happen.
I load the sitemap in a modal, that has the Google font loaded: the modal-generated title is in the Google font. If you wish to see for yourself, the link to the site is: https://advisory-council-degas.com/Main/
and the sitemap pops up after clicking the picture of the climbing man.

Kind regards, Benno