I often use “ch” as a unit when sizing paragraph widths, to give a maximum characters wide. When I go to type this, I will type
“80ch” – which is then stored in the styles as “80chpx” 
But when I type
“20rem” – which is recognized and parsed into “20” and the units changed to “rem”.
Not urgent. I can work around it. Probably only the major unit missing at this point and well-supported? ch (character) unit | Can I use... Support tables for HTML5, CSS3, etc