mojo::dom::css

.out

[
  [
    'tag', 'p', { id => 'a' }, [
      'tag', 'div', {}, [ 'root', $_->[0][3] ], $_->[0], [
        'tag', 'p', { id => 'b' }, $_->[0][3],
        [ 'text', 123, $_->[0][3][5] ],
      ],
    ], [ 'text', 'Test', $_->[0] ],
  ], $_->[0][3][5],
]

.pl

#!/usr/bin/env perl
use strict;
use warnings;
use Data::Dumper::Compact qw(ddc);
use Mojo::DOM ();
use Mojo::DOM::CSS ();
my $dom = Mojo::DOM->new('<div><p id="a">Test</p><p id="b">123</p></div>');
my $css = Mojo::DOM::CSS->new(tree => $dom->tree);
my $elements = $css->select('p');
print ddc $elements;