Check out example codes for "CSS adding background image from file". It will help you in understanding the concepts better.

Code Example 1

/* Answer to: "add background image css" */

/*
  The background-image property sets one or more background images
  for an element.

  By default, a background-image is placed at the top-left corner
  of an element, and repeated both vertically and horizontally.

  Tip: The background of an element is the total size of the
  element, including padding and border (but not the margin).

  Tip: Always set a background-color to be used if the image is
  unavailable.
*/

/* Set a background-image for the <body> element: */

body {
 background-image: url("paper.gif");
 background-color: #cccccc;
}

/* Set two background images for the <body> element: */

body {
  background-image: url("img_tree.gif"), url("paper.gif");
  background-color: #cccccc;
}

Code Example 2

/* The first method using an image on your server */
background: url('img/someimage.jpg');

/* The second method using an image hosted on another server */
background: url('http://www.someimage.com/someimage.jpg');

/* A third method that allows the site to determine protocol instead of explicitly defining it */
background: url('//www.someimage.com/someimage.jpg');

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