App.xaml

<Application x:Class="MP3joiner.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                          xmlns:materialDesign="http://materialdesigninxaml.net/winfx/xaml/themes"
             xmlns:local="clr-namespace:MP3joiner"
             StartupUri="MainWindow.xaml">
    <Application.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <!-- Material Design's ResourceDictionaries -->

                <materialDesign:BundledTheme BaseTheme="Light" PrimaryColor="BlueGrey" SecondaryColor="Lime"/>
                <!--<ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.Light.xaml"/>-->
                <ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesign3.Defaults.xaml"/>

                <!-- Other dictionaries -->
            </ResourceDictionary.MergedDictionaries>

            <Style BasedOn="{StaticResource MaterialDesignRaisedButton}" TargetType="{x:Type Button}">
                <Setter Property="materialDesign:ButtonAssist.CornerRadius" Value="20" />
            </Style>

            <!--<Style TargetType="{x:Type Button}" BasedOn="{StaticResource {x:Type Button}}">
                <Setter Property="materialDesign:ButtonAssist.CornerRadius" Value="10" />
            </Style>-->
        </ResourceDictionary>
    </Application.Resources>
</Application>