If you inspect your page with Firefox Web Developer tool (get that!) you'll see a warning:
[13:36:48.725] The stylesheet http://home.ca.astound.net/~m.dewilde/style.css was not loaded because its MIME type, "text/html", is not "text/css". @ http://home.ca.astound.net/~m.dewilde/
so either you have an error in your HTML (seems ok to me) or you need to add that MIME type to your webserver so that it will send the right content-type with the .css file.
if you are on a Apache server add this to your .htaccess:
AddType text/css .css
/edit:
Since you are using the HTML5 doctype you can safely omit the type="text/css" bit
try <link rel="stylesheet" href="style.css" >
not that I expect this to make a difference, but since the confusion seesm to be about the MIME type worth trying