Step 1:Add a reference to HandyControl or search for HandyControl on the nuget;
Step 2:Add code in App.xaml as follows:
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="pack://application:,,,/HandyControl;component/Themes/SkinDefault.xaml"/>
<ResourceDictionary Source="pack://application:,,,/HandyControl;component/Themes/Theme.xaml"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
Step 3:enjoy coding