Issues with responsivness on small screens / smartphones

Hello,

I’m having issues with the Ultra theme on smartphones and small windows. When the window is getting smaller then a certain size, a black bar appears on the right side of the website. Please check http://outsideit.net/naf_update_nsclient_scripts_folder/ for an example. Am I doing something wrong?

I tried setting custom css

img { max-width: 75%; height: auto; }

But it doesn’t help. I also tried disabling comments, but it also didn’t help. Any help is highly appreciated.

Greetings.

Willem