Add temporary hook to allow themes to update the layout styles.

modules/layout/a12s_layout.module

@@ -185,8 +185,9 @@ function a12s_layout_preprocess_paragraph(array &$variables): void {
     $layoutId = $paragraph->getBehaviorSetting('layout_paragraphs', 'layout');
 
     if ($layoutId) {
-      $displayOptions = $paragraph->getBehaviorSetting('layout_paragraphs', ['config', 'display_options'], []);
-      DisplayTemplatePluginManager::preprocessVariables('layout:' . $layoutId, 'paragraph', $displayOptions, $variables);
+      $config = $paragraph->getBehaviorSetting('layout_paragraphs', 'config', []);
+      DisplayTemplatePluginManager::preprocessVariables('layout:' . $layoutId, 'paragraph', $config['display_options'] ?? [], $variables);
+      // @todo add module and theme alter as in a12s_layout_preprocess_layout()?
     }
   }
 
@@ -221,8 +222,19 @@ function a12s_layout_preprocess_layout(array &$variables): void {
   }
 
   if ($variables['layout'] instanceof LayoutDefinition) {
-    $displayOptions = $variables['settings']['display_options'] ?? [];
+    $config = $variables['settings'] ?? [];
+    $displayOptions = $config['display_options'] ?? [];
     DisplayTemplatePluginManager::preprocessVariables('layout:' . $variables['layout']->id(), 'layout', $displayOptions, $variables);
+
+    // @todo find a better way to manipulate variables and layouts...
+    // Allow modules and themes to change the processed variables.
+    $context = [
+      'layout_id' => $variables['layout']->id(),
+      'config' => $config,
+    ];
+
+    \Drupal::moduleHandler()->alter('a12s_layout_layout_variables', $variables, $context);
+    \Drupal::theme()->alter('a12s_layout_layout_variables', $variables, $context);
   }
 }
 

modules/layout/src/Plugin/A12sLayoutDisplayOptionsSet/GridLayout.php

@@ -51,8 +51,12 @@ class GridLayout extends DisplayOptionsSetPluginBase {
     return $form;
   }
 
-  /* @todo manage column_breakpoint
-  function preprocessVariables(array &$variables, array $configuration = [])
+  function preprocessVariables(array &$variables, array $configuration = []): void {
     parent::preprocessVariables($variables, $configuration);
-  ... */
+
+    if (!empty($configuration['column_breakpoint']) && $configuration['column_breakpoint'] !== '_all') {
+      $this->addClasses($variables['attributes'], 'column-breakpoint-' . $configuration['column_breakpoint']);
+    }
+  }
+
 }