Check out example codes for "css set background color". It will help you in understanding the concepts better.

Code Example 1

body {
  background-color: green;
}

Code Example 2

body {
	background-color: red; 
}

Code Example 3

body {
  background-color: rgb(255,255,255);
}

Code Example 4

body {
  background-color: lightblue;
}

Code Example 5

body {
  /* this changes the page's background to green  */
  background-color: green;
}

Learn ReactJs, React Native from akashmittal.com