As a web developer in the past I found - though maybe that has changed in recent years, let me know if that is the case - there aren't any real resolution-indep

As a web developer in the past I found - though maybe that has changed in recent years, let me know if that is the case - there aren't any real resolution-independent units you can use to design an interface that is comfortable on every medium. You can peg your design to things like viewport width or font size, but you always end up having to make an arbitrary decision at some point, because there is no way for the web browser to know the physical dimensions of the screen the webpage is actually being displayed on. You have to make educated guesses based on the relationship between width and height, user agent and other headers, stuff like that, and create different stylesheets for each case. The style for the 1920x1080 screen (rotated horizontally) of the smallest smartphones can't have the same font size as the style of a 1920x1080 30 inch desktop monitor.