App.xaml

<Application x:Class="WpfCssStyle.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:WPF="clr-namespace:WpfCssStyle"
             StartupUri="MainWindow.xaml">
    <Application.Resources>
        <!-- Sizes -->
        <Style x:Key="size12" TargetType="Label">
            <Setter Property="FontSize" Value="12" />
        </Style>
        <Style x:Key="size16" TargetType="Label">
            <Setter Property="FontSize" Value="16" />
        </Style>
        <Style x:Key="size24" TargetType="Label">
            <Setter Property="FontSize" Value="24" />
        </Style>
        <!-- Bold/Italic -->
        <Style x:Key="bold" TargetType="Label">
            <Setter Property="FontWeight" Value="ExtraBold" />
        </Style>
        <Style x:Key="italic" TargetType="Label">
            <Setter Property="FontStyle" Value="Italic" />
        </Style>
        <!-- Colors -->
        <Style x:Key="gray" TargetType="Label">
            <Setter Property="Foreground" Value="#333333" />
        </Style>
        <Style x:Key="royalBlue" TargetType="Label">
            <Setter Property="Foreground" Value="RoyalBlue" />
        </Style>
        <Style x:Key="green" TargetType="Label">
            <Setter Property="Foreground" Value="Green" />
        </Style>
        <Style x:Key="yellow" TargetType="Label">
            <Setter Property="Foreground" Value="Yellow" />
        </Style>
        <Style x:Key="red" TargetType="Label">
            <Setter Property="Foreground" Value="#D00000" />
        </Style>
        <!-- Fonts -->
        <Style x:Key="verdana" TargetType="Label">
            <Setter Property="FontFamily" Value="Verdana" />
        </Style>
        <Style x:Key="georgia" TargetType="Label">
            <Setter Property="FontFamily" Value="Georgia" />
        </Style>
        <!-- Effects -->
        <Style x:Key="shadow" TargetType="Label">
            <Setter Property="Effect">
                <Setter.Value>
                    <DropShadowEffect ShadowDepth="0" />
                </Setter.Value>
            </Setter>
        </Style>
        <!-- Predefined Combinations -->
        <Style x:Key="h1" TargetType="{x:Type Label}"
               BasedOn="{WPF:CssStyle Names='size24 royalBlue'}" />
        <Style x:Key="warning" TargetType="{x:Type Label}"
               BasedOn="{WPF:CssStyle Names='size24 yellow bold shadow'}">
            <Setter Property="BorderThickness" Value="1" />
            <Setter Property="BorderBrush" Value="Yellow" />
        </Style>
    </Application.Resources>
</Application>