my %template_variables = (
    'navytext' => $navytext,
    # ...
);

my $css = <<'CSS';
#tabmenu {
          color: #$navytext;
         }
CSS

sub fill_template {
    my( $str, $vars ) = @_;
    $str =~ s!\$(\w+)!$template{ $1 } || '$' . $1!ge;
    $str
};

print fill_template( $css , \%template_variables );