Add customized HTML, CSS & JavaScript

1. Edit Confluence page, add HTML Macro for Confluence macro, paste the below example to macro body

<style>

  div#box {
    background-color: lightgrey;  
    border: 2px solid green;
    border-radius:5px;
    padding: 10px;
    margin: 10px;
  }

</style>
<script>
  console.log('HTML Macro');
</script>

<div id="box">This text is the content of the box. We have added a
 10px padding, 10px margin and a 2px green border. Ut enim ad minim veniam,
 quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo
 consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse 
 cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat
 cupidatat non proident, sunt in culpa qui officia deserunt mollit
 anim id est laborum.</div>

2. Publish Confluence page and see the result