Adjusting font size

Hi all, I’m having trouble adjusting the font within the “Jumbo Headline” section within my theme. I’m using the Matheson theme. I am trying to change the font and size of the text under ‘Title’ and ‘Text’, both of which are apart of customizing the jumbo headline.

I found that trying to change the size by styling h3 or p does not work within the wordpress theme customizer, and I’ve also tried adding custom css but I must not be getting the right code changed.

Any and all help would be appreciated. Here is my site: http://www.bfaccc.com/