Em values for font sizes and line spacing
Em values allows me to set relative values for font sizes and line spacing in a way that the line spacing is always relative and proportional to the font size. This is a great time saver.
Please take a look at Typecast, you can set it in px and/or em. Amazingly flexible.
Joel Meine commented
Some additional notes for the XD Dev team ---
When considering how to integrate VW, VH, % and EM values into XD, With the new Web Development CSS Snippets within the Design Specs Output, if XD allowed the designer to set the CSS Base Font Size in PX (to compute the appropriate EM conversion, - and - allow a checkbox to output thee CSS current PX value as EM or % (Possibly even by object, component or group may be more effective - as some values are set as a percent and some as an EM or PX in the same web project)
This would make the Copy and Paste snippet much more valuable for developers as there would be less need to hand-modify, once it has been copied from XD.
Tash H commented
If I could, I would upvote @Adam m Babkes' comment.
All of this. Also percentage-based line-height would be incredible to go with this.
Chris Cannon commented
Have a different sizing types rather than just pixels.
On web - VW, %, VH, EM REM, PT.
It would be also great to reflect that in design specs - this way by setting a rem base you could have all other values calculated automaically and the developers could see the exact rem value to put into CSS.
Adam M Babkes commented
It is crucial in responsive design to be able to use ems and percentage to identify size and line height. Potentially VW and VH as well. Ideally, it'd be nice to create designs with viewport change in mind so as not to leave it solely to the developer to decide how they are executed.
Using Rem and Em units.