Issue #3471352 by naveenvalecha: Handle modification for contain image style in ImageBgModifier.

Closes #3471352

modules/modifiers_bg_image/src/Plugin/modifiers/ImageBgModifier.php

@@ -34,6 +34,11 @@ class ImageBgModifier extends ModifierPluginBase {
             $args['size'] = 'cover';
             break;
 
+          case 'contain':
+            $args['size'] = $config['image_style'];
+            $args['repeat'] = 'no-repeat';
+            break;
+
           case 'no-repeat':
           case 'repeat':
           case 'repeat-x':