The preferred way to avoid the <FONT> tag and take advantage of styles sheets is to use <SPAN>. And, as luck would have it, CGI.pm supports span (if you import the :html3 definitions).

use CGI qw(:standard :html3);
...
print span({-style => 'Color: red;'}, "I'm an error value!");
[download]

Or, to do this with style sheets:

use CGI qw(:standard :html3);
...
print span({-class => 'Error'}, "I'm an error value!");
[download]

I'll leave getting the style sheet defined as an open-book excercise. Reading the CGI.pm POD is allowed and encouraged.