KeyboardAudioVisualizer/KeyboardAudioVisualizer/UI/Visualization/LevelVisualization.xaml

<styles:CachedResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                                 xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                                 xmlns:styles="clr-namespace:KeyboardAudioVisualizer.Styles"
                                 xmlns:visualizationProvider="clr-namespace:KeyboardAudioVisualizer.AudioProcessing.VisualizationProvider"
                                 xmlns:visualization="clr-namespace:KeyboardAudioVisualizer.UI.Visualization">

    <styles:CachedResourceDictionary.MergedDictionaries>
        <styles:CachedResourceDictionary Source="/KeyboardAudioVisualizer;component/Styles/FrameworkElement.xaml" />
        <styles:CachedResourceDictionary Source="/KeyboardAudioVisualizer;component/Styles/Theme.xaml" />
    </styles:CachedResourceDictionary.MergedDictionaries>

    <Style x:Key="StyleLevelVisualizer" 
           BasedOn="{StaticResource StyleFrameworkElement}"
           TargetType="{x:Type visualization:LevelVisualizer}">
        <Setter Property="Height" Value="64" />
        
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type visualization:LevelVisualizer}">
                    <Grid>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="*" />
                            <ColumnDefinition Width="*" />
                        </Grid.ColumnDefinitions>

                        <Border Grid.Column="0" BorderThickness="0,0,1,0" BorderBrush="White">
                            <Border x:Name="BrdLeft" Background="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=BrushLeft}">
                                <Border.OpacityMask>
                                    <VisualBrush>
                                        <VisualBrush.Visual>
                                            <Border Width="{Binding ElementName=BrdLeft, Path=ActualWidth}"
                                                    Height="{Binding ElementName=BrdLeft, Path=ActualHeight}"
                                                    Background="Transparent">
                                                <Rectangle HorizontalAlignment="Right" Fill="Black" 
                                                           Width="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=SizeLeft}" />
                                            </Border>
                                        </VisualBrush.Visual>
                                    </VisualBrush>
                                </Border.OpacityMask>
                            </Border>
                        </Border>

                        <Border Grid.Column="1" BorderThickness="1,0,0,0" BorderBrush="White">
                            <Border  x:Name="BrdRight" Background="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=BrushRight}">
                                <Border.OpacityMask>
                                    <VisualBrush>
                                        <VisualBrush.Visual>
                                            <Border Width="{Binding ElementName=BrdRight, Path=ActualWidth}"
                                                    Height="{Binding ElementName=BrdRight, Path=ActualHeight}"
                                                    Background="Transparent">
                                                <Rectangle HorizontalAlignment="Left" Fill="Black"
                                                           Width="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=SizeRight}" />
                                            </Border>
                                        </VisualBrush.Visual>
                                    </VisualBrush>
                                </Border.OpacityMask>
                            </Border>
                        </Border>
                    </Grid>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

    <DataTemplate DataType="{x:Type visualizationProvider:LevelVisualizationProvider}">
        <visualization:LevelVisualizer Style="{StaticResource StyleLevelVisualizer}" VisualizationProvider="{Binding}" />
    </DataTemplate>

</styles:CachedResourceDictionary>