As per How to properly use css-values viewport-relative-lengths?, I don't think it's correct to use viewport units outside of restricting them with @media
queries for minimum height and width of the viewport, and even then, I think it should only be used when you know that the page they'll be applying to is very small (e.g. a business-card style page), and would otherwise leave the whole viewport screen empty handed.
In other words, what exactly are you looking for when you say font-size: 5.3vmin
?
What if I cascade multiple windows one by one, only leaving enough room in each viewport as to see three lines of normal text? The text at 5.3vmin
will be so small at to be unintelligible!
Likewise, if I have a huge monitor (say, Seiki 39" @ 3840x2160, which, I must point out, is quite affordable at below 400 USD), and you use font-size: 5.3vmin
for all your headers on a page with a lengthy article, then you're stripping my ability and comfort to fully enjoy all the extra lines of text that my monitor can support, instead having 5 headers occupy more than a quarter of the screen, which instead could have been filled by a hundred of extra lines of text.