App.xaml

<Application x:Class="sShell.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:local="clr-namespace:sShell"
             StartupUri="pack://application:,,,/Windows/SplashScreen.xaml">
    <Application.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary 
                Source="pack://application:,,,/Styles/Themes/DarkTheme.xaml"/>
                <ResourceDictionary 
                Source="pack://application:,,,/Styles/GenericStyles.xaml"/> 
                <ResourceDictionary 
                Source="pack://application:,,,/Styles/ScrollViewer.xaml"/>
                <ResourceDictionary 
                Source="pack://application:,,,/Styles/TreeView.xaml"/>
                <ResourceDictionary 
                Source="pack://application:,,,/Styles/ComboBox.xaml"/>
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Application.Resources>
</Application>