That solves a different problem. REM is useful for making the value relative to a master value; v-units make the value relative to the viewport.<p>I actually use the two in conjunction. I set some my html {font-size: 1.2vw;} (or whatever), and all type in the document to 1rem (or whatever measurement). Then I finally step out the html size to major browser breakpoints using old-fashioned media queries.