How to link JavaScript and HTML5 pages without tag?

I am trying to make a button for my webpage that changes the ENTIRE colour palette of the page with Code.org AppLab. The only problem is, code.org doesn’t allow the use of the <script> tag for “security reasons”. As far as I know the only way I can turn on CSS settings with a button is with getElementById(). If anyone knows how to activate CSS settings when a button is clicked without JS, how to link external JS files to an html file, or use inline JS all WITHOUT the use of the <script> tag please show me how. Any help would be greatly appreciated.

I’m begging someone to help me PLEASE.