I think you are using ASCX transformation. Please try to change your transformation from ASCX to text/xml and try below code snippet.
Here I mentioned example for Text/ XML transformation How to handle div with background conditionally -
{%if(MenuItemName == "Home"){ %}
<div style="background:red">
<p>Back ground is red</p>
{%} else {%}
<div >
<p>No Back ground color</p>
{%}#%}
</div>
NOTE: GetFileUrl is not support in Kentico 11 and it is changed from GetFileUrl to GetAttachmentUrlByGUID.
API changes Reference URL:https://devnet.kentico.com/documentation/api-changes/kentico-11/24985
Other way handling DIV with Multiple Backgrounds:
<div style="background: url('<%# GetFileUrl("BgBanner") %>'), url('<%# GetFileUrl("BgImage") %>');background-repeat: no-repeat, repeat;background-size: 100% auto contain;">
<p>Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh euismod tincidunt ut laoreet dolore magna aliquam erat volutpat.</p>
<p>Ut wisi enim ad minim veniam, quis nostrud exerci tation ullamcorper suscipit lobortis nisl ut aliquip ex ea commodo consequat.</p>
</div>
https://www.w3schools.com/css/css3_backgrounds.asp
https://stackoverflow.com/questions/11468604/multiple-backgrounds-with-different-background-size