CSS To turn off display of sidebars and footers on mobile devices.

I thought that adding the following to my style.CSS of my child theme would turn off display of my sidebars and footers on devices with a width of 320 or less. But this is not working as desired. Can you please point out my error?

site = temp.avmi.net
attempted css addition:

@media screen and (max-width: 320px) {
#sidebar, #footer {
	display: none;
	}
}

Thanks!