what is the correct format of defining background image in css3 code example

Example 1: html background image

<!-- Code by Scratchy -->
<!-- Twitter: @S_cratchy-->

<head>
  <style>
    body {
      background-image: url(https://wallup.net/wp-content/uploads/2019/09/110394-cats-grey-kittens-fluffy-fat-grass-animals-cat-kitten-baby-cute-748x468.jpg) 
    }
  </style>
  
  <body>
    You have set the background image!
    
    
    
  </body>

Example 2: make image background of div

background-image: url("photographer.jpg");

Example 3: adding background image css

/* Answer to: "adding 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;
}