[newbie] Trouble adding script to dynamically change CSS values based on conditions

Support
4

Alright, I placed the code that @cpradio suggested in a CSS/HTML Customization page under the tab, but unfortunately it doesn’t seem to be working. Just to prove the concept, I have it try to display an alert. Below is the exact code I am using:

<script type="text/discourse-plugin">

import { withPluginApi } from 'discourse/lib/plugin-api';

function initializePlugin(api)
{
  api.onPageChange((url, title) => {
        alert('test');
  });
}

export default {
  name: 'align-category-text',
  initialize: function(container)
  {
    withPluginApi('0.1', api => initializePlugin(api));
  }
};

</script>

I made sure the code was enabled and tried restarting rails. Any thoughts on what I’m missing?