with no dtd you are limited to html2
self closed elements (end in /> ) are xhtml ONLY
the declaration of your css wil lbe ignored
if you make the firstline of the html file a dtd for html 4 (strict or transitional) or xhtml (strict or transitional) you will be able to properly use external css files <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> sample html4 Transitional DTD
course notes are never complete
whitespace and indenting are not required for production code and should be removed
often 40-50% of the filesize downloaded to the user browser is whitespace
Its ok as an aid to developer, but a code highlighting notepad is better.