Help me guys!!

Yall! I'm kinda struggiling to change my notification icon. I've tried multiple codes from different people, but it doesn't seem to change and it stays as the golden bell. Has anyone had that problem before, and if yes, than how did you fix it (if you did obviously)?

By the way, my code looks like this:

<style>

li.active .icon { content:url('https://i.pinimg.com/736x/05/a9/4d/05a94d18d9a553e4c7d018deec862693.jpg'); width: 20PX;height: 20px;}

</style>