CSS:
.thisElement {
background-image: url('/img/backgrounds/image.jpg');
}
HTML:
<body class="thisElement">...</body>
Use the CSS class/id to call your image and then create the element you want the image to be on (div, header, body, etc) and add that class/id to the element.
CSS Class and ID examples:
Class Example:
.thisClass {
background-image: url('/img/backgrounds/image.jpg');
}
ID Example:
#thisID {
background-image: url('/img/backgrounds/image.jpg');
}
HTML example calling the css
<div class="thisClass">...</div>
<div id="thisID">...</div>