Hello Laura,
Sorry for the troubles you are having with the dropdown overflowing. I can help you out with this.
Thanks for the link and I took a look at your site.
There is a script running on your site called Chosen that is adding a classes such as “chzn-container” to the select boxes causing it to show.
Perhaps it is from the theme or a plugin?
Anyway I was able to come up with this css that I got working to hide it.
.tribe-bar-views-inner .chzn-container-single {
display:none;
}
It should work, but since the reason it is showing because of a script there is a chance it may not.
Let me know if it works or you would like some more help, thanks.