PowerToys/src/settings-ui/Settings.UI/Styles/TextBlock.xaml

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

    <Style x:Key="OobeSubtitleStyle" TargetType="TextBlock">
        <Setter Property="Margin" Value="0,16,0,0" />
        <Setter Property="Foreground" Value="{ThemeResource DefaultTextForegroundThemeBrush}" />
        <Setter Property="AutomationProperties.HeadingLevel" Value="Level3" />
        <Setter Property="FontFamily" Value="XamlAutoFontFamily" />
        <Setter Property="FontSize" Value="{StaticResource BodyTextBlockFontSize}" />
        <Setter Property="FontWeight" Value="SemiBold" />
        <Setter Property="TextTrimming" Value="CharacterEllipsis" />
        <Setter Property="TextWrapping" Value="Wrap" />
        <Setter Property="LineStackingStrategy" Value="MaxHeight" />
        <Setter Property="TextLineBounds" Value="Full" />
    </Style>

    <x:Double x:Key="SecondaryTextFontSize">12</x:Double>
    <Style x:Key="SecondaryTextStyle" TargetType="TextBlock">
        <Setter Property="FontSize" Value="{StaticResource SecondaryTextFontSize}"/>
        <Setter Property="Foreground" Value="{ThemeResource TextFillColorSecondaryBrush}"/>
    </Style>

    <x:Double x:Key="HeaderTextFontSize">12</x:Double>
    <Style x:Key="HeaderTextStyle" TargetType="TextBlock">
        <Setter Property="FontSize" Value="{StaticResource HeaderTextFontSize}"/>
        <Setter Property="Foreground" Value="{ThemeResource TextFillColorSecondaryBrush}"/>
        <Setter Property="FontWeight" Value="Bold" />
    </Style>
</ResourceDictionary>