App.xaml

<Application x:Class="BertUI.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             StartupUri="MainWindow.xaml">
    <Application.Resources>

        <Style x:Key="LaunchButton" TargetType="{x:Type Button}">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type Button}">
                        <Grid>
                            <Rectangle x:Name="rectangle" Fill="{TemplateBinding Background}"/>
                            <ContentPresenter 
                                HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" 
                                VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                                RecognizesAccessKey="True" 
                                SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" 
                            />
                        </Grid>
                        <ControlTemplate.Triggers>
                            <Trigger Property="IsFocused" Value="True" >
                            	<Setter Property="Stroke" TargetName="rectangle" Value="White"/>
                            	<Setter Property="StrokeThickness" TargetName="rectangle" Value="3"/>
                            </Trigger>
                            <Trigger Property="IsDefaulted" Value="True"/>
                            <Trigger Property="IsMouseOver" Value="True" />
                            <Trigger Property="IsPressed" Value="True"/>
                            <Trigger Property="IsEnabled" Value="False"/>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
            <Setter Property="Background" Value="Black" />
            <Setter Property="FontSize" Value="18px" />
            <Setter Property="Foreground" Value="White" />
            <Setter Property="BorderBrush" Value="{x:Null}" />
            <Setter Property="VerticalContentAlignment" Value="Bottom" />
            <Setter Property="HorizontalContentAlignment" Value="Center" />
            <Setter Property="FocusVisualStyle" Value="{x:Null}" />
        </Style>
    </Application.Resources>
</Application>