Add the view mode to the CSS classes used for the body
If you are using sub theme of bootstrap theme then you can possibly add class to body tag of the node.

Go to SubThemeDirectory/and open template.php and add this hook_preprocess_html()

function THEMENAME_preprocess_html(&amp;$vars) {
  if ($node = menu_get_object()) {
    $vars['body_attributes_array']['class'][] = 'mode-' . $vars['page']['content']['system_main']['nodes'][$node-&gt;nid]['#view_mode']; // Node ID class
  }
}


I hope this'll at least give an idea how to add class attribute.