<Application x:Class="Your project"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:AduSkin="https://github.com/aduskin">
    <Application.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <AduSkin:AduSkinTheme ThemeType="Light"/> 
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Application.Resources>
</Application>