diff --git a/core/modules/ckeditor/lib/Drupal/ckeditor/Plugin/ckeditor/plugin/Internal.php b/core/modules/ckeditor/lib/Drupal/ckeditor/Plugin/ckeditor/plugin/Internal.php
index 3a3ac28..753ad6e 100644
--- a/core/modules/ckeditor/lib/Drupal/ckeditor/Plugin/ckeditor/plugin/Internal.php
+++ b/core/modules/ckeditor/lib/Drupal/ckeditor/Plugin/ckeditor/plugin/Internal.php
@@ -53,7 +53,6 @@ public function getConfig(Editor $editor) {
       'customConfig' => '', // Don't load CKEditor's config.js file.
       'pasteFromWordPromptCleanup' => TRUE,
       'justifyClasses' => array($rtl ? 'align-right' : 'align-left', 'align-center', $rtl ? 'align-left' : 'align-right', 'align-justify'),
-      'coreStyles_underline' => array('element' => 'span', 'attributes' => array('class' => 'underline')),
       'removeDialogTabs' => 'image:Link;image:advanced;link:advanced',
       'resize_dir' => 'vertical',
       'keystrokes' =>  array(
diff --git a/core/modules/ckeditor/lib/Drupal/ckeditor/Tests/CKEditorTest.php b/core/modules/ckeditor/lib/Drupal/ckeditor/Tests/CKEditorTest.php
index b4d52ab..d0b2af7 100644
--- a/core/modules/ckeditor/lib/Drupal/ckeditor/Tests/CKEditorTest.php
+++ b/core/modules/ckeditor/lib/Drupal/ckeditor/Tests/CKEditorTest.php
@@ -225,7 +225,6 @@ protected function getDefaultInternalConfig() {
       'customConfig' => '',
       'pasteFromWordPromptCleanup' => TRUE,
       'justifyClasses' => array('align-left', 'align-center', 'align-right', 'align-justify'),
-      'coreStyles_underline' => array('element' => 'span', 'attributes' => array('class' => 'underline')),
       'removeDialogTabs' => 'image:Link;image:advanced;link:advanced',
       'resize_dir' => 'vertical',
       'keystrokes' =>  array(array(0x110000 + 75, 'link'), array(0x110000 + 76, NULL)),
diff --git a/core/modules/system/system.base.css b/core/modules/system/system.base.css
index c40d552..4029a64 100644
--- a/core/modules/system/system.base.css
+++ b/core/modules/system/system.base.css
@@ -289,9 +289,6 @@ input {
 .align-justify {
   text-align: justify;
 }
-.underline {
-  text-decoration: underline;
-}
 
 /**
  * Block-level HTML5 display definition.