Inspired by the original CSS proposal, which includes "weighting" of each rule or style sheet, and generates a weighted average:
/* user styles */
html { font-size: 16px 60%; }
/* author styles (40% remaining) */
html { font-size: 3vw; }
I've given the user font-size a weight of 60%,
and my own `72px` font-size
a weight of 40%.