Disable zoom when focus in input on mobile

Add this in your child-theme’s style.css:

@media only screen and (max-device-width: 480px) {

     input {
          font-size: 16px;
     }
}

16px appears to be the optimal font-size for reading on mobile devices. Consequently, the mobile devices stop to zoom when 16px is set as the font-size for inputs.

Source: https://jonassebastianohlsson.com/blog/2013/11/25/how-to-stop-zoom-in-on-input-focus-on-mobile-devices/