CSS for mobile optimization fonts?

Recently I’ve installed like three different mobile plug-ins for see how they work and only one of them worked at all. Although I don’t entirely like how it changes my website on mobile, I do like how it forces the font to be a specific size. Can someone help me figure out what CSS code I would need to force the fonts of the page title, headers, and normal text/paragraph text to be a specific size for mobile users? The text size I use is far too large on mobile but the perfect size I think for desktop. I’m currently using WP mobile pack but don’t like how it makes my website look on mobile unless you’re actually on a specific page. Also, I have CSS code already that makes my text and everything bold already no matter what, and I hope I don’t have to get rid of that. Also, my website is theloudsoul.com. I wasn’t sure where else to post this. I wan’t to force the font a different size for mobile users only and leave it where it’s at for desktop.