my $log = Mojo::Log->new; ## Or use $app->log . . .

my $orig_result = $ua->get( $url )->result;
if( $orig_result->is_success ) {
  my $dom = $orig_result->dom;
  my $target = $dom->at( q{...} )->attr( q{src} );

  if( $target ) {
    my $save_result = $ua->get( q{https:} . $target )->result;
    if( $save_result->is_success ) {
      $save_result->save_to( q{target.jpg} );
    } else {
      $log->error( qq{Problem fetching target '$target': },
                   $save_result->code, q{ },
                   $save_result->message );      
    }
  } else {
    $log->error( qq{Unable to locate CSS target in '$url'} );
  }
} else {
  $log->error( qq{Problem fetching '$url': }, 
               $orig_message->code, 
               q{ }, $orig_result->message )
}