HTML or Markdown block inherit font sizing

I'm trying to create a simple code (or markdown) block where I modify the color of a single word or phrase. Think something like:

<div style="text-align:center;">
Look at this <span style="color:red;">colorful</span> text
</div>

If I try to apply <h> tags it overrides the colors, and if I try to size it manually it is not mobile responsive.

Is there a way to make my text inherit the responsive size properties of my already defined <h> sizes?

you changed span to h tag?