vh - viewport height
vw - viewport width
vmin - viewport min
vmax - viewport max
1 viewport unit = 1% of the viewport axis
So, 1vh = 1% of the total viewport height
And, 1vmin = 1vh or 1vw, whichever is smaller
And, 1vmax = 1vh or 1vw, whichever is larger
setting font-size: 3vw; = setting one char to 3% of the viewport width