device width

1body {
2  background: white;    
3}
4 
5@media screen and (min-width: 980px) /* Desktop */ {
6  body {
7    background: red;
8  }
9}
10 
11@media screen  and (max-width: 979px) /* Tablet */ {
12  body {
13    background: blue;
14  }
15}
16 
17@media screen and (max-width: 500px) /* Mobile */ {
18  body {
19    background: green;
20  }
21}
22