It's like @Kleith mentions, just a rule of 3 and I quote:
The value in
em , applied in a formula would be something like
valorEnPixles / padreEnPixeles , in your example,
26 / 30 eso da 0.86em .
Now you must remember, that the idea of using
ems , is precisely not recalculating the inherited measures, so that they are "pixel perfect" and doing that calculation would always be a lost time, above all if you are all the time manipulating the base measure of the parent container. It simply has no case.
What I recommend, is that you are not clear yet, is to look for examples, why it is currently recommended to use "
em " instead of
pixel in certain cases and change "the ship" in the form of layout, because you are pretending to use a dynamic measure as if it were a static measure and the truth, if you really need to use specific measures, it will always be better to use the measure directly in
pixeles and not in