An em is a measurement similar to px, except that it is based on the size of the text rather than a specific number of pixels. As a very rough guide, 1em is around 16 px, though that will vary a lot. Another way to think of it is that it’s the width of the letter “m”.
the function/importance of this line:
" a{display:inline;} /* for IE;*/"
It’s a hack to help older versions of Internet Explorer.
Thanks Ralph. Do I understand it correctly that apart form 1 “em” being roughly 16px, there is not difference in the working i.e. if I subsitute 320 px by 20 em, the result will be pretty much the same?
I like using EMs because in WEB DESIGN the end user has control over font size. In other word if grandma cant see she can press a button and poof the default size goers from 16px to 80px. If you set measurements in px in your css they stay that size, but EMs are relative to the current container font size, insuring the layout retains most of it’s proportions regardless of the user’s chosen font size.
To add to theabove, there are lots of informative threads about this around here, such as this one: