CSS overriding for dropdowns

Hey guys!

I am using the event plus plugin for my website and it looks like Highend is overriding css for dropdowns.

You can see the problem on this link : http://www.kaenel-autoecole.ch/evrplus_registration/?action=evrplusegister&event_id=4

When the users want to select the number of tickets (below) they would like to buy they can’t click on the field. They would have to go on the very left (above “prix”) to be able to select but basically no one would do that.

The plugin support told me the problem was to be solved on your side.

Can you please help?

Thanks a lot!
Patrick