Make Excerpt Text Size Responsive?

I’m making my site as responsive as possible, so I need basically everything to alter for different screen sizes…

The problem is, the [EXCERPT] shortcode comes with it’s own set of styles, so the font size can’t be changed for different screen sizes.

I’ve tried wrapping the shortcode with a <p class=” “> tag using my own class, but nothing changes – even when my class uses !important tags.

Long story short – is there any way I can make the excerpt text smaller for smaller screen sizes? This should be simple…