Check out example codes for "css fill div with background image". It will help you in understanding the concepts better.

Code Example 1

html { 
  background: url(images/bg.jpg) no-repeat 
    center center fixed; 
  -webkit-background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  background-size: cover;
}

Code Example 2

div {
  background-image: url("example.com/image.png");
  background-size: 100% 100%;
}

Code Example 3

/* with CSS 3 */
#yourdiv {  
    background: url('bgimage.jpg') no-repeat;
    background-size: 100%;
}

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