@todeepthydon Great. That's a way to add labels to the Rich Text content. But as I mentioned earlier, you could not style in the Prismic editor. Prismic kits render a custom label as a <span> with a label as a class name on the front, and you need to apply CSS to this classname.
I hope it answers your questions. Let me know if you've any further questions.
Thanks,
Priyanka