> Can you answer me some questions, if it's not too much work.
Not much work ... but I'm not in front of a computer-screen all day so
can't always respond quickly :-)
> Why we have to change from pixel to em measure units? It's more
> browser friendly or W3C friendly? It's only for height values?
Goes better with font-size/line-height. Font-size/line-height defaults
differ across browser-land, which is basically what caused the "1px off"
problem in the first place. By letting all browsers know that they
should calculate dimensions to font-size no matter what that font-size
actually is, they'll cover up for their differences.
> We should use line-height instead of what? Why do we have to use
> line-height and height, all together?
Not "instead of" anything, really, although it replaces vertical padding
in your case. The right line-height automatically introduces vertical
adjustment to text in those short "lines", so adjusting the text with
vertical paddings becomes unnecessary. Vertical padding would otherwise
be added to height and throw off any alignment.
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