How to attach browser-specific stylesheets in D8?
I think this'll do it in Drupal 7, it should be the same for Drupal 8:

$build['#attached']['css'][] = array(
  'type' =&gt; 'file',
  'data' =&gt; $path_to_css,
  'options' =&gt; array(
    'browsers' =&gt; array(
      'IE' =&gt; 'lte IE 9',
      '!IE' =&gt; FALSE,
    ),
  ),
 );