Yes! There's a couple of different ways you could do this. Both ways are generally simple to implement.
The first way is the (enchant:) macro. If you've used it before you may know that it can change selected text based on its content or hook name. In Harlowe 2.0 and onward, you can use the following code
(enchant:?Page, (color:#000000) + (background:#ffffff))
to change the page and text color easily. This can also be manipulated by (if:) statements, since it's a macro, and is very useful when combined with the "header" tag! However, fair warning: (enchant:) is the nemesis of (live:) for the most part, and will refresh (causing the screen to flash) every time the live command activates.
Paste this in your header passage:
(if: (passage:)'s tags's length > 0)[
(print: "<script>$('tw-story').addClass('" + (passage:)'s tags.join(' ') + "'\)</script>")
And add this to story stylesheet (bottom-left menu, but you probably knew that)
XXX should be the passage tag in all passages you want to format.
I hope this helps!