[Plugin: Leaflet Maps Marker] Transparent pop-up text marker

Hi,

First of all, I would like to thank you for this plugin: REALLY GREAT!

I need help with this page:
https://www.concorsorosatiditalia.it/?page_id=59

The “text box” containing the text of the marker is transparent.
Is there any particular reason?
I can solve by forcing the css?

thank you very much

https://www.ads-software.com/extend/plugins/leaflet-maps-marker/