π Font sizing with rem (archive)
Defining font sizes in px gives you control but it prevents the user from increasing the font size on some browsers (till IE9). em is more accessible and allows for resizing, but since the unit is relative to the font size of its parent it has a compounding effect which is hard to manage.
The rem unit is relative only to the root html element’s font size. By setting the html‘s font size to 62.5% you can use rems almost like px, in that 1.4rem would be 14px (because 62.5 Γ 1.6 = 100, 16px being the usual browser default text size)