I was playing around with my demo environment and modified the wallpaper to give it a nice Nutanix branding.

Here’s the result:

To do this simply edit the file C:\Inetpub\wwwroot\Citrix\CitrixWeb\contrib\custom.style file. The “CitrixWeb” part might be different depending on your store naming when you configured Storefront.

Make it look like this:

/* Edit this file to customize the User Interface by overriding the existing CSS Styles. 
* You can use browser development tools to identify the CSS classes you want to customize.
*/

/* When using the StoreFront Authentication SDK to return custom forms, a class "customform" is added to each form.
* The following commented CSS rule illustrates how to modify the width of form field labels for custom forms.
*/

body {
background-image: url("nutanix.jpg");
}

/*
.customform .field {
width: 400px;
}

/* Logon box font color, size and alignment. */ #logonbox-logonform label{ 
color:white; 
display:table-cell; 
font-size:12px; 
}
*/

Then drop in your background graphic in the same folder, and done!