App.xaml

<Application x:Class="SettingsManager.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:componentModel="clr-namespace:System.ComponentModel;assembly=PresentationFramework"
             xmlns:local="clr-namespace:SettingsManager"
             StartupUri="MainWindow.xaml">
    <Application.Resources>

        <FontFamily x:Key="QuadratGrotesk">pack://application:,,,/Fonts/#QuadratGroteskNewW03-Rg</FontFamily>
        <FontFamily x:Key="QuadratGroteskBold">pack://application:,,,/Fonts/#QuadratGroteskNewW03-Bold</FontFamily>

        <ImageBrush x:Key="BackgroundImage" ImageSource="pack://application:,,,/Images/spacewave.png" Stretch="UniformToFill"/>

        <Style x:Key="DesignerBlackBackgroundStyle">
            <Style.Triggers>
                <Trigger Property="componentModel:DesignerProperties.IsInDesignMode"
                         Value="True">
                    <Setter Property="Control.Background" Value="{StaticResource BackgroundImage}" />
                </Trigger>
            </Style.Triggers>
        </Style>
    </Application.Resources>
</Application>