Wino-Mail/Wino.Core.WinUI/AppThemes/Snowflake.xaml

<ResourceDictionary
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:xaml="using:Microsoft.UI.Xaml">

    <x:String x:Key="ThemeName">Snowflake</x:String>
    <x:String x:Key="ThemeBackgroundImage">ms-appx:///Wino.Core.WinUI/BackgroundImages/Snowflake.jpg</x:String>

    <ImageBrush x:Key="WinoApplicationBackgroundColor" ImageSource="{StaticResource ThemeBackgroundImage}" />
    <SolidColorBrush x:Key="AppBarBackgroundColor">Transparent</SolidColorBrush>

    <ResourceDictionary.ThemeDictionaries>
        <ResourceDictionary x:Name="Light">
            <!--  Brushes  -->
            <SolidColorBrush x:Key="MailListHeaderBackgroundColor">#b0c6dd</SolidColorBrush>
        </ResourceDictionary>
        <ResourceDictionary x:Name="Dark">
            <!--  Brushes  -->
            <SolidColorBrush x:Key="MailListHeaderBackgroundColor">#b0c6dd</SolidColorBrush>
        </ResourceDictionary>
    </ResourceDictionary.ThemeDictionaries>
</ResourceDictionary>