Can someone please explain to me what's happenned to the fonts when you're developing a web application? I''ve got my .css file and it reads as per below. *** does 1em and 2em and 3em mean? I can understand that you can manually change things to 10pt etc, but would like to know what em means. Also, is there a way to make it default to pt?

cheers.

Code:
BODY
{
	font-weight: normal;
	font-size: 8pt;
	word-spacing: normal;
	text-transform: none;
	font-family: Verdana, Helvetica, sans-serif;
	letter-spacing: normal;
	background-color: white;
}

H1, H2, H3, H4, H5, TH, THEAD, TFOOT
{
    COLOR: #003366;
}
H1	{	
	font-family: Verdana, Arial, Helvetica, sans-serif;
	font-size: 2em;
	font-weight:	700;
	font-style:	normal;
	text-decoration:	none;
	word-spacing:	normal;
	letter-spacing:	normal;
	text-transform:	none;
	}	
		
H2
{
	font-weight: bold;
	font-size: 10pt;
	word-spacing: normal;
	text-transform: none;
	font-style: normal;
	font-family: Verdana, Arial, Helvetica, sans-serif, 'Trebuchet MS';
	letter-spacing: normal;
	text-decoration: none;
}