examples/dockwidgets/MyTitleBar_CSS.h - add multiple include guard

examples/dockwidgets/MyTitleBar_CSS.h

@@ -9,6 +9,11 @@
   Contact KDAB at <info@kdab.com> for commercial licensing options.
 */
 
+#ifndef EXAMPLETITLEBAR_CSS_H
+#define EXAMPLETITLEBAR_CSS_H
+
+#pragma once
+
 #include <kddockwidgets/private/widgets/TitleBarWidget_p.h>
 
 /**
@@ -77,3 +82,5 @@ public:
 MyTitleBar_CSS::~MyTitleBar_CSS()
 {
 }
+
+#endif