JSFiddle - React, Tailwind, and code Playground

HTML

<html xmlns:customtag>
    <style> 
        @media all {  
          customtag\:someElement { 
            width:100px; 
            height: 100px; 
            background: blue; 
            display: block; 
          } 
          customtag\:someOtherElement { 
            width: 50px; 
            height: 50px; 
            background: red; 
            display: block; 
          }
        }
    </style>
    <customtag:someElement id='tester'>test</customtag:someElement>
    <customtag:someOtherElement>test</customtag:someOtherElement>
</html>

JavaScript

$('#tester').animate({opacity: .3},1000);