core/modules/ckeditor/ckeditor.module              |  1 +
 .../filter/src/Plugin/Filter/FilterAlign.php       |  7 +++-
 .../Drupal/FunctionalTests/Theme/ClassyTest.php    |  6 +--
 core/themes/classy/classy.info.yml                 |  3 ++
 core/themes/classy/classy.theme                    | 17 --------
 core/themes/classy/css/components/filter.align.css |  2 +-
 core/themes/classy/src/ProcessedText.php           | 49 ----------------------
 7 files changed, 13 insertions(+), 72 deletions(-)

diff --git a/core/modules/ckeditor/ckeditor.module b/core/modules/ckeditor/ckeditor.module
index b05df2e3cc..fb7fd83658 100644
--- a/core/modules/ckeditor/ckeditor.module
+++ b/core/modules/ckeditor/ckeditor.module
@@ -72,6 +72,7 @@ function ckeditor_ckeditor_css_alter(array &$css, Editor $editor) {
   // editor uses the filter_align filter. This is used by the included
   // CKEditor DrupalImage plugin, the media module's DrupalMedia plugin, by
   // blockquote elements, et. al.
+  // @see core/modules/filter/filter.libraries.yml
   if ($filters->has('filter_align') && $filters->get('filter_align')->status) {
     $css[] = drupal_get_path('module', 'filter') . '/css/filter.align.css';
   }
diff --git a/core/modules/filter/src/Plugin/Filter/FilterAlign.php b/core/modules/filter/src/Plugin/Filter/FilterAlign.php
index a3739ab824..7b384b9d33 100644
--- a/core/modules/filter/src/Plugin/Filter/FilterAlign.php
+++ b/core/modules/filter/src/Plugin/Filter/FilterAlign.php
@@ -40,7 +40,12 @@ public function process($text, $langcode) {
           $node->setAttribute('class', implode(' ', $classes));
         }
       }
-      $result->setProcessedText(Html::serialize($dom));
+      $result->setProcessedText(Html::serialize($dom))
+        ->addAttachments([
+          'library' => [
+            'filter/align',
+          ],
+        ]);
     }
 
     return $result;
diff --git a/core/tests/Drupal/FunctionalTests/Theme/ClassyTest.php b/core/tests/Drupal/FunctionalTests/Theme/ClassyTest.php
index 00601137d1..eb8447609e 100644
--- a/core/tests/Drupal/FunctionalTests/Theme/ClassyTest.php
+++ b/core/tests/Drupal/FunctionalTests/Theme/ClassyTest.php
@@ -37,9 +37,7 @@ public function testRegressionMissingMessagesCss() {
   }
 
   /**
-   * Tests that classy/align library is added conditionally.
-   *
-   * @see \Drupal\classy\ProcessedText::preRender().
+   * Tests that the classy/align library override of filter/align is loaded.
    */
   public function testFilterAlignCss() {
     $this->container
@@ -57,7 +55,7 @@ public function testFilterAlignCss() {
       'type' => 'blog',
       'title' => "Compassion: that's the one things no machine ever had.",
       'body' => [
-        'value' => 'Highly illogical.',
+        'value' => '<blockquote data-align="center">Highly illogical.</blockquote>',
         'format' => 'test_format',
       ],
     ]);
diff --git a/core/themes/classy/classy.info.yml b/core/themes/classy/classy.info.yml
index 161b539475..0954e4250c 100644
--- a/core/themes/classy/classy.info.yml
+++ b/core/themes/classy/classy.info.yml
@@ -26,5 +26,8 @@ libraries-extend:
   media/media_embed_ckeditor_theme:
     - classy/media_embed_ckeditor_theme
 
+libraries-override:
+  filter/align: classy/align
+
 ckeditor_stylesheets:
   - css/components/media-embed-error.css
diff --git a/core/themes/classy/classy.theme b/core/themes/classy/classy.theme
deleted file mode 100644
index 8595946de8..0000000000
--- a/core/themes/classy/classy.theme
+++ /dev/null
@@ -1,17 +0,0 @@
-<?php
-
-/**
- * @file
- * Functions to support theming in the Classy theme.
- */
-
-use Drupal\classy\ProcessedText;
-
-/**
- * Implements hook_element_info_alter().
- */
-function classy_element_info_alter(array &$info) {
-  if (array_key_exists('processed_text', $info)) {
-    $info['processed_text']['#pre_render'][] = [ProcessedText::class, 'preRender'];
-  }
-}
diff --git a/core/themes/classy/css/components/filter.align.css b/core/themes/classy/css/components/filter.align.css
index 4254aa23b2..153545cbd0 100644
--- a/core/themes/classy/css/components/filter.align.css
+++ b/core/themes/classy/css/components/filter.align.css
@@ -1,6 +1,6 @@
 /**
  * @file
- * Align filter: default styling for displaying aligned images, media, etc.
+ * Override of core/modules/filter/css/filter.align.css.
  */
 
 /**
diff --git a/core/themes/classy/src/ProcessedText.php b/core/themes/classy/src/ProcessedText.php
deleted file mode 100644
index 21eba31e38..0000000000
--- a/core/themes/classy/src/ProcessedText.php
+++ /dev/null
@@ -1,49 +0,0 @@
-<?php
-
-namespace Drupal\classy;
-
-use Drupal\Core\Security\TrustedCallbackInterface;
-use Drupal\filter\Entity\FilterFormat;
-
-/**
- * Class to hold trusted callback for processed text.
- */
-class ProcessedText implements TrustedCallbackInterface {
-
-  /**
-   * Preprocesses processed text to add additional libraries conditionally.
-   *
-   * @param array $element
-   *   An associative array containing the properties and children of the
-   *   element.
-   *
-   * @return array
-   *   The modified element with added library.
-   */
-  public static function preRender(array $element) {
-    if (!isset($element['#format'])) {
-      return $element;
-    }
-
-    $format = FilterFormat::load($element['#format']);
-
-    if (empty($format)) {
-      return $element;
-    }
-
-    $filter_align = $format->filters('filter_align');
-    if ($filter_align && $filter_align->status) {
-      $element['#attached']['library'][] = 'classy/align';
-    }
-
-    return $element;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public static function trustedCallbacks() {
-    return ['preRender'];
-  }
-
-}