Issue #2330465 by rachel_norfolk: Fixed Remove entity_reference.admin.css.

core/modules/entity_reference/css/entity_reference.admin.css

-
-.entity_reference-settings {
-  margin-left: 1.5em; /* LTR */
-}
-[dir="rtl"] .entity_reference-settings {
-  margin-right: 1.5em;
-}

core/modules/entity_reference/src/ConfigurableEntityReferenceItem.php

@@ -197,9 +197,6 @@ public function instanceSettingsForm(array $form, FormStateInterface $form_state
 
     $form = array(
       '#type' => 'container',
-      '#attached' => array(
-        'css' => array(drupal_get_path('module', 'entity_reference') . '/css/entity_reference.admin.css'),
-      ),
       '#process' => array(
         '_entity_reference_field_instance_settings_ajax_process',
       ),