CrouchingBruin on "[Theme: Corpo] Header, prefooter sizing problem with mobile view"

The problem is that you've added some custom CSS for the header & footer, which is overriding the CSS for the media query which controls the responsiveness. All you need to do is recopy the media query to the end of your custom CSS:

/* All Mobile Sizes (devices and browser) */
@media only screen and (max-width: 767px) {
   #wrapper {width: 100%; margin: 0 auto; padding: 10px 0;}
   #header, #footer {
      overflow: hidden;
      width: auto;
      position: static;
      padding: 0 20px;
     }