DiscordChatExporter/DiscordChatExporter.Gui/App.xaml

<Application
    x:Class="DiscordChatExporter.Gui.App"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:DiscordChatExporter.Gui"
    xmlns:materialDesign="http://materialdesigninxaml.net/winfx/xaml/themes"
    xmlns:s="https://github.com/canton7/Stylet">
    <Application.Resources>
        <s:ApplicationLoader>
            <!--  Bootstrapper  -->
            <s:ApplicationLoader.Bootstrapper>
                <local:Bootstrapper />
            </s:ApplicationLoader.Bootstrapper>

            <!--  Merged dictionaries  -->
            <ResourceDictionary.MergedDictionaries>
                <!--  Colors are irrelevant because they are overriden in runtime  -->
                <materialDesign:BundledTheme
                    BaseTheme="Light"
                    PrimaryColor="Blue"
                    SecondaryColor="Blue" />

                <ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.Defaults.xaml" />
            </ResourceDictionary.MergedDictionaries>

            <!--  Styles  -->
            <Style x:Key="MaterialDesignRoot" TargetType="{x:Type Control}">
                <Setter Property="FontFamily" Value="{DynamicResource MaterialDesignFont}" />
                <Setter Property="RenderOptions.BitmapScalingMode" Value="HighQuality" />
                <Setter Property="SnapsToDevicePixels" Value="True" />
                <Setter Property="TextElement.FontSize" Value="13" />
                <Setter Property="TextElement.FontWeight" Value="Regular" />
                <Setter Property="TextElement.Foreground" Value="{DynamicResource MaterialDesignBody}" />
                <Setter Property="TextOptions.TextFormattingMode" Value="Ideal" />
                <Setter Property="TextOptions.TextRenderingMode" Value="Auto" />
                <Setter Property="UseLayoutRounding" Value="True" />
            </Style>

            <Style BasedOn="{StaticResource MaterialDesignScrollBarMinimal}" TargetType="{x:Type ScrollBar}" />

            <Style BasedOn="{StaticResource MaterialDesignLinearProgressBar}" TargetType="{x:Type ProgressBar}">
                <Setter Property="BorderThickness" Value="0" />
                <Setter Property="Background" Value="Transparent" />
                <Setter Property="Foreground" Value="{DynamicResource SecondaryAccentBrush}" />
                <Setter Property="Height" Value="2" />
                <Setter Property="Maximum" Value="1" />
                <Setter Property="Minimum" Value="0" />
            </Style>

            <Style BasedOn="{StaticResource MaterialDesignTextBox}" TargetType="{x:Type TextBox}" />

            <Style BasedOn="{StaticResource MaterialDesignComboBox}" TargetType="{x:Type ComboBox}" />

            <Style BasedOn="{StaticResource MaterialDesignDatePicker}" TargetType="{x:Type DatePicker}" />

            <Style BasedOn="{StaticResource MaterialDesignTimePicker}" TargetType="{x:Type materialDesign:TimePicker}" />

            <Style
                x:Key="MaterialDesignFlatDarkButton"
                BasedOn="{StaticResource MaterialDesignFlatButton}"
                TargetType="{x:Type Button}">
                <Style.Resources>
                    <SolidColorBrush x:Key="MaterialDesignFlatButtonClick" Color="#4C4C4C" />
                </Style.Resources>

                <Setter Property="Foreground" Value="{DynamicResource PrimaryHueMidForegroundBrush}" />
            </Style>

            <Style
                x:Key="MaterialDesignFlatActionToggleButton"
                BasedOn="{StaticResource MaterialDesignActionToggleButton}"
                TargetType="{x:Type ToggleButton}">
                <Setter Property="Background" Value="Transparent" />
                <Setter Property="Foreground" Value="{DynamicResource PrimaryHueMidBrush}" />

                <Style.Triggers>
                    <Trigger Property="IsMouseOver" Value="True">
                        <Setter Property="Background" Value="{DynamicResource MaterialDesignFlatButtonClick}" />
                        <Setter Property="BorderBrush" Value="{DynamicResource MaterialDesignFlatButtonClick}" />
                    </Trigger>
                </Style.Triggers>
            </Style>

            <!--  Default MD Expander is incredibly slow (https://github.com/MaterialDesignInXAML/MaterialDesignInXamlToolkit/issues/1307)  -->
            <Style BasedOn="{StaticResource MaterialDesignExpander}" TargetType="{x:Type Expander}">
                <Setter Property="Template">
                    <Setter.Value>
                        <ControlTemplate TargetType="Expander">
                            <Border BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}">
                                <DockPanel Background="{TemplateBinding Background}">
                                    <ToggleButton
                                        Name="HeaderSite"
                                        BorderThickness="0"
                                        Content="{TemplateBinding Header}"
                                        ContentStringFormat="{TemplateBinding HeaderStringFormat}"
                                        ContentTemplate="{TemplateBinding HeaderTemplate}"
                                        ContentTemplateSelector="{TemplateBinding HeaderTemplateSelector}"
                                        Cursor="Hand"
                                        DockPanel.Dock="Top"
                                        Focusable="False"
                                        Foreground="{TemplateBinding Foreground}"
                                        IsChecked="{Binding Path=IsExpanded, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}"
                                        IsTabStop="False"
                                        Opacity=".87"
                                        Style="{StaticResource MaterialDesignExpanderDownHeaderStyle}"
                                        TextElement.FontSize="15" />
                                    <Border
                                        Name="ContentSite"
                                        DockPanel.Dock="Bottom"
                                        Visibility="Collapsed">
                                        <StackPanel
                                            Name="ContentPanel"
                                            Margin="{TemplateBinding Padding}"
                                            HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                                            VerticalAlignment="{TemplateBinding VerticalContentAlignment}">
                                            <ContentPresenter
                                                Name="PART_Content"
                                                ContentStringFormat="{TemplateBinding ContentStringFormat}"
                                                ContentTemplate="{TemplateBinding ContentTemplate}"
                                                ContentTemplateSelector="{TemplateBinding ContentTemplateSelector}"
                                                Focusable="False" />
                                        </StackPanel>
                                    </Border>
                                </DockPanel>
                            </Border>
                            <ControlTemplate.Triggers>
                                <Trigger Property="IsExpanded" Value="true">
                                    <Setter TargetName="ContentSite" Property="Visibility" Value="Visible" />
                                </Trigger>
                                <Trigger Property="ExpandDirection" Value="Right">
                                    <Setter TargetName="HeaderSite" Property="DockPanel.Dock" Value="Left" />
                                    <Setter TargetName="ContentSite" Property="DockPanel.Dock" Value="Right" />
                                    <Setter TargetName="ContentPanel" Property="Orientation" Value="Horizontal" />
                                    <Setter TargetName="ContentPanel" Property="Height" Value="Auto" />
                                    <Setter TargetName="HeaderSite" Property="Style" Value="{StaticResource MaterialDesignExpanderRightHeaderStyle}" />
                                </Trigger>

                                <Trigger Property="ExpandDirection" Value="Left">
                                    <Setter TargetName="HeaderSite" Property="DockPanel.Dock" Value="Right" />
                                    <Setter TargetName="ContentSite" Property="DockPanel.Dock" Value="Left" />
                                    <Setter TargetName="ContentPanel" Property="Orientation" Value="Horizontal" />
                                    <Setter TargetName="ContentPanel" Property="Height" Value="Auto" />
                                    <Setter TargetName="HeaderSite" Property="Style" Value="{StaticResource MaterialDesignExpanderLeftHeaderStyle}" />
                                </Trigger>

                                <Trigger Property="ExpandDirection" Value="Up">
                                    <Setter TargetName="HeaderSite" Property="DockPanel.Dock" Value="Bottom" />
                                    <Setter TargetName="ContentSite" Property="DockPanel.Dock" Value="Top" />
                                    <Setter TargetName="ContentPanel" Property="Orientation" Value="Vertical" />
                                    <Setter TargetName="ContentPanel" Property="Width" Value="Auto" />
                                    <Setter TargetName="HeaderSite" Property="Style" Value="{StaticResource MaterialDesignExpanderUpHeaderStyle}" />
                                </Trigger>

                                <Trigger Property="ExpandDirection" Value="Down">
                                    <Setter TargetName="HeaderSite" Property="DockPanel.Dock" Value="Top" />
                                    <Setter TargetName="ContentSite" Property="DockPanel.Dock" Value="Bottom" />
                                    <Setter TargetName="ContentPanel" Property="Orientation" Value="Vertical" />
                                    <Setter TargetName="ContentPanel" Property="Width" Value="Auto" />
                                    <Setter TargetName="HeaderSite" Property="Style" Value="{StaticResource MaterialDesignExpanderDownHeaderStyle}" />
                                </Trigger>
                            </ControlTemplate.Triggers>
                        </ControlTemplate>
                    </Setter.Value>
                </Setter>
            </Style>
        </s:ApplicationLoader>
    </Application.Resources>
</Application>