What is best replacement for in CSS?

Answer 1

from W3C

http://www.w3.org/TR/html4/present/graphics.html#edef-FONT

size = cdata [CN] Deprecated.

This attribute sets the size of the font. Possible values:

• An integer between 1 and 7. This sets the font to some fixed size, whose rendering depends on the user agent. Not all user agents may
  render all seven sizes.
• A relative increase in font size. The value "+1" means one size larger. The value "-3" means three sizes smaller. All sizes belong to the scale of 1 to 7.

front this peice you could clearly see that equivalent to size will be large or x-large .. etc

explanation :

is just as if you used font-size: medium ;

is just as if you used font-size: large ;

is just as if you used font-size: x-large ;

is just as if you used font-size: xx-large ;

is just as if you used font-size: -webkit-xxx-large;

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update :

i think i have got it wrong the first time it's not em's (although they work similarly). please see the update :)