Mobile site header font size problems

I need to reduce the font size of the text of the header in the mobile version of my site. I am trying to use the new platform.  The font size for the mobile header seems locked into the desktop site header. Unfortunately, this makes the mobile site look like it was a preschool project!  
Why can I not simply highlight the text with a mouse and change the font size?  The name of the site is slafer2016B.homesteadcloud.com.

Thank-you