That’s why you’re having problems in the 960px view (which is what you see in Tablet Landscape. If you set that container to 1200px, everything inside of it will be off and not be responsive.
I’d recommend removing the 1200px and using basic containers as containers because they will work responsively with different devices. Then add this code to activate the 1200px media query:
This will automatically size your container to 1200px on bigger monitors, not 960px resolutions.