Menu disappears completely on mobile screens

Is there a way to have the navigation menu still display on a mobile screen? (like an icon with dashed lines, drop down or anything).

I tried this code that was posted in another thread but it did not work

/* Adjustments for the menu display on smaller devices like the iPhone 4 */
@media only screen and (max-device-width: 480px) {
	.main-navigation,
	    .main-navigation ul ul {
		width: 324px;
	}
}