Size content to viewport error from Google on WordPress site

I am getting this message from Google Pagespeed insights:

The page content is too wide for the viewport, forcing the user to scroll horizontally. Size the page content to the viewport to provide a better user experience.

The page content is 5,305 CSS pixels wide, but the viewport is only 320 CSS pixels wide. The following elements fall outside the viewport:

<div class="full_bg full-width-bg">We build Brand…technologies.</div>

But when I view any mobile devices, it load properly. How do I fix this? Many thanks in advance! ??

The site is at https://urlgone.com/f7d291/