أنشئ حسابًا أو سجّل الدخول للانضمام إلى مجتمعك المهني.
Please read this article http://css-tricks.com/css-media-queries/
In general media queries is to define a responsive layout of your website on different devices such as tablet , mobile , tv ....
Also note that you can avoid using a lot of media query to match your demand by using float , width , margin attributes ....