You could use the viewport units in css to scale the font. The units are vw for viewport width and vh for viewport height. Use these as units for your CSS font sizes where the number will correspond to a % of the viewport width (or height) like so:
p {
font-size: 4vw;
}
Of course, you are maybe better if that variable comes from a max-of that value and the minimum value for a decent readable font-size .. even thou at 320px wide, you'll get something like 12px font-size ..