my $line_in = <<EOT;
<?xml-stylesheet href="perl1.css" type="text/css"?>
<link href="//www.perl.org/css/perl1.css" rel="stylesheet">
<link href="/css/perl.css" rel="stylesheet">
EOT

##</code><code>##

my @ss = $line_in =~ m{<(.*?)stylesheet(.*?)>}gis;

##</code><code>##

  $1                         $2
|----|          |--------------------------------|
<?xml-stylesheet href="perl1.css" type="text/css"?>
                    $1                                   $2
 |--------------------------------------------|          |
<link href="//www.perl.org/css/perl1.css" rel="stylesheet">
                $1                        $2
 |-----------------------------|          |
<link href="/css/perl.css" rel="stylesheet">

##</code><code>##

my @ss = $line_in =~ m/(href="[^"]+")/gi;
print "$_\n" for @ss;
#
# href="perl1.css"
# href="//www.perl.org/css/perl1.css"
# href="/css/perl.css"

##</code><code>##

my @ss = $line_in =~ m/<(?=[^>]*stylesheet).*(href="[^">]+")/gis;