Spotfire HTML Text Area got a native Insert JavaScript option, which is great for adding reusable JavaScript code.
On similar pattern, it would be great to add "Insert CSS" option as well to -
Create Reusable stylesheets to be added. This will help us to add same css style to all/multiple pages.
Using central stylesheet will attract low maintenance effort, as any update will be needed in at single place only.
Make HTML text area more cleaner while editing, by reducing lines of codes for css.
Redistribution of standard stylesheets will be easier.