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

Code Example 1

<!-- Background images are better implemented in CSS -->
<!-- but here is how you could do it in HTML in a pinch -->

<head>
  <style>
    .background {
      background-image: url(https://cleananddelicious.com/wp-content/uploads/2016/03/Avocad0-CD.jpg);
    }
  </style>
</head>

<body>
  <div class=background>
    <h1>The background of this div will be an avocado</h1>
  </div>
</body>

Code Example 2

<style>
body {
  background-image: url('img_girl.jpg');
  background-repeat: no-repeat;
  background-attachment: fixed;
  background-size: cover;
}
</style>

Code Example 3

<!-- 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>

Code Example 4

html,body {
  background-image: url("your.picture");
}

Code Example 5

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

Code Example 6

/* 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;
}

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