:before selector not adding content - html

Question

I'm trying to add an image before other images. It should be before every image except the first one. So thought of adding it like:
.class3:not(:first-child):before {
background-image: url('image.jpg');
width: 2rem;
height: 2rem;
}
The html gets added dynamically through Backbone and uses Handlebars. It looks something like this:
<div class="class1">
<div class="class2">
{{#each item}}
<div class="class3" style="background-image: url('{{image1}}')">
<p>{{text}}</p>
<img class="dialog-popup-rewards" src={{image2}} />
</div>
{{/each}}
</div>
</div>
But nothing gets added. I tested the before statement with less complexity. Adding a before to all of the divs:
.class3:before {
background-color: black;
width: 2rem;
height: 2rem;
}
And it never gets added. What am I missing? I rewrote the code for the sake of clarity, so I might have slipped in some syntax errors.
Would it be better to try this with a Handlebars helper?
Thank you in advance.

Answer 1

You need to include a content property in your :before css block. It can be just an empty string. Try this for your simplified example:
.class3:before {
content: '';
background-color: black;
width: 2rem;
height: 2rem;
}