Check out example codes for "css media queries". It will help you in understanding the concepts better.

Code Example 1

@media only screen and (max-width: 1200px){
    /*Tablets [601px -> 1200px]*/
}
@media only screen and (max-width: 600px){
	/*Big smartphones [426px -> 600px]*/
}
@media only screen and (max-width: 425px){
	/*Small smartphones [325px -> 425px]*/
}

Code Example 2

/* Sur les écrans, quand la largeur de la fenêtre fait au maximum 1280px */
@media screen and (max-width: 1280px)

/* Sur tous types d'écran, quand la largeur de la fenêtre est comprise entre 1024px et 1280px */
@media all and (min-width: 1024px) and (max-width: 1280px)

/* Sur les téléviseurs */
@media tv

/* Sur tous types d'écrans orientés verticalement */
@media all and (orientation: portrait)

Code Example 3

/* 
  Extra small devices (phones, 600px and down) */
@media only screen and (max-width: 600px) 
  {...} 

/* Small devices (portrait tablets and large phones, 600px and up) 
  */
@media only screen and (min-width: 600px) {...} 

/* Medium devices (landscape tablets, 768px and up) */

  @media only screen and (min-width: 768px) {...} 

/* Large devices (laptops/desktops, 992px and up) 
  */

  @media only screen and (min-width: 992px) {...} 

/* Extra large devices (large 
  laptops and desktops, 
  1200px and up) */
@media only screen and (min-width: 1200px) {...}

Code Example 4

CSS @media Rule

Example
Change the background color of the <body> element to "lightblue" when the browser window is 600px wide or less:

Syntax
@media only screen and (max-width: 600px) {
  body {
    background-color: lightblue;

    }
}

Code Example 5

@media only screen and (max-width: 600px) {
  body {
    background-color: lightblue;
  }
}

Code Example 6

body {
  background: white;    
}

@media screen and (min-width: 980px) /* Desktop */ {
  body {
    background: red;
  }
}

@media screen  and (max-width: 979px) /* Tablet */ {
  body {
    background: blue;
  }
}

@media screen and (max-width: 500px) /* Mobile */ {
  body {
    background: green;
  }
}

Learn ReactJs, React Native from akashmittal.com