my $button1 = $mw->Button(-text => "18-Letters",
                          -command => sub {print OUTFILE "18L\n", background => "yellow"})->pack(-side =>"top");

##</code><code>##

my $button1 = $mw->Button(-text => "18-Letters",
                          -command => sub {print OUTFILE "18L\n" },
                          -background => "yellow"})->pack(-side =>"top");

##</code><code>##

sub { print OUTFILE "18L\n", background => "yellow" }

##</code><code>##

sub { print OUTFILE "18L\n", "background", "yellow" }