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correctly specifying css font-size

w3cschools tells us to use

body { font-size:100%; }

for a default size of 16px (if the user didn’t change his browsers settings, which then would probably be for a good reason) and the further font size specifying as em

* { font-size:xem; }

As IE (the main problem yet again) won’t correctly resize px.

em = px / 16

so

px = 16 * em