CSS validation

[John Creech]

Web gurus,

I am still thrashing w/ CSS and am stumped. I have a style sheet that
validates at the W3C validator, but I keep getting one warning that I
can't shake.  I've waded through most of the warnings and have fixed them,
but this one I don't get.  Say I want to declare: 

H1 
{
	font-family:  Verdana, "san-serif";
	font-size : 20pt;
	margin-top : 1em;  
	color: #550000;
	background : transparent;
	text-align: center;
}

The warning I get is " You are encouraged to offer a generic family as a
last alternative : H1" - anybody up for explaining this?  TIA.

John Creech
Electronic Resources & Systems Librarian
Central Washington University Library 
400 E. 8th Ave. | Ellensburg, WA 98926 | 
office - 509-963-1081 || fax - 509-963-3684
creechj at www.lib.cwu.edu