Fixes #5424: `Html::addCssStyle()` wasn't correctly setting style passed in array

framework/CHANGELOG.md

@@ -10,6 +10,7 @@ Yii Framework 2 Change Log
 - Bug #5323: Nested dropdown does not work for `yii\bootstrap\DropDown` (aryraditya)
 - Bug #5336: `yii\bootstrap\DropDown` should register bootstrap plugin asset (zelenin)
 - Bug #5379: `Module::afterAction()` was called even when `beforeAction()` returned false (cebe)
+- Bug #5424: `Html::addCssStyle()` wasn't correctly setting style passed in array (kartik-v, samdark) 
 - Bug: Date and time formatting now assumes UTC as the timezone for input dates unless a timezone is explicitly given (cebe)
 - Enh #4040: Added `$viewFile` and `$params` to the `EVENT_BEFORE_RENDER` and `EVENT_AFTER_RENDER` events for `View` (qiangxue) 
 - Enh #4275: Added `removeChildren()` to `yii\rbac\ManagerInterface` and implementations (samdark)

framework/helpers/BaseHtml.php

@@ -1703,9 +1703,9 @@ class BaseHtml
                     }
                 }
             }
-            $style = static::cssStyleFromArray(array_merge($oldStyle, $newStyle));
+            $style = array_merge($oldStyle, $newStyle);
         }
-        $options['style'] = $style;
+        $options['style'] = is_array($style) ? static::cssStyleFromArray($style) : $style;
     }
 
     /**