Question one is resolved.
I found out that I can change the font-sizes in my custom style sheet.
About question two.
What I want to change is the footer layout (.grid-33, .tablet-grid-33 and .mobile-grid-33), into something like this for the desktops:
And into something like this for the tablets and mobiles:
When I put this in my custom css this works on my desktop, but how can I make the different css work on my tablet en mobile?