To do this you’re going to have to have FTP access to your server that the site is hosted on (or someway to upload files).
Open up an editor program on your computer (Notepad) will work and copy/paste the following into the file.
<?php
/**
Template Name: Page with background only
*/
?>
<html>
<head>
<link rel="stylesheet" href="<?php bloginfo('stylesheet_url'); ?>" type="text/css" media="screen" />
<style type="text/css">
body { background-color: #cccccc; background-image: url('https://uffekirkegaard.dk/wp-content/uploads/2010/10/bg.jpg'); background-repeat: repeat-y; background-position: top center; background-attachment: scroll; }
#page-content { width: 800px; margin: 20px auto; }
</style>
<title><?php wp_title( '|', true, 'right' ); bloginfo('url'); ?></title>
<?php wp_head(); ?>
</head>
<body>
<?php while (have_posts()) : the_post(); ?>
<div id="page-content">
<?php the_content(); endwhile; ?>
</div>
</body>
</html>
Then, save this file on your computer with something like the name of background-only.php. Then log into your server and upload this file into the folder of the current theme you are using.
Which for you would be /wp-content/themes/Uffes Child/
Once you have done that, log into your WordPress installation and create a new page. On the right hand side under the Publish button make sure you select the ‘Page with background only’ option from the dropdown list.
You could do a lot more with this but this is a pretty basic stripped down version.