Add style container bar

source/Component/CommandBar/CommandBar.scss

@@ -10,6 +10,7 @@ div.command-bar {
         text-align: center;
         display: flex;
         justify-content: center;
+        transition: all 100ms ease-in-out;
         color:  inherit;
         
         span.ms-Button-flexContainer i.ms-Icon {

source/Component/CommandBar/CommandBar.tsx

@@ -14,7 +14,7 @@ class CommandBar extends Component<ICommandBarProps> {
     render(): ReactNode {
         return <Theme
             className="command-bar"
-            backgroundLevel={BackgroundLevel.Level3}
+            backgroundLevel={BackgroundLevel.Level2}
             style={{ width: this.props.width }}
         >
             <div>
@@ -43,7 +43,7 @@ class CommandBar extends Component<ICommandBarProps> {
             i18nKey={param.i18NKey}
             directionalHint={DirectionalHint.rightCenter}
         >
-            <IconButton 
+            <IconButton
                 style={{ height: this.props.width }}
                 iconProps={{ iconName: param.iconName }}
                 onClick={ param.click }