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

Code Example 1

body {
  background-color: green;
}

Code Example 2

/* To apply color to background you have to use 'background-color' property and value of property is color name. */
html,body {
  background-color: blue;
}

Code Example 3

body {
  background-color: lightblue;
}

Code Example 4

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

Code Example 5

html,body {
  background-color: red;
}

Code Example 6

div {
 opacity:25% ; 
}

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