Adding CSS to a CGI script

I am curious about adding CSS to a CGI script, lets say that this is my script

~~~~~~~
#!/usr/bin/perl
use warnings;
use strict;
use CGI qw(:standard);
print header(), start_html("Add Me");
print h1("Add Me");
if(param()) {
  my $n1 = param('field1');
  my $n2 = param('field2');
  my $n3 = $n2 + $n1;
  print p("$n1 + $n2 = <strong>$n3</strong>\n");
} else {
  print hr(), start_form();
  print p("First Number:", textfield("field1"));
  print p("Second Number:", textfield("field2"));
  print p(submit("add"), reset("clear"));
  print end_form, hr();
}
print end_html();
~~~~~~~

Would it be possible to add CSS when handling HTML like that?