CopyDemoAvalonia/TestRepeat/App.axaml

<Application xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             x:Class="TestRepeat.App"
             xmlns:local="using:TestRepeat"
             RequestedThemeVariant="Default">
             <!-- "Default" ThemeVariant follows system theme variant. "Dark" or "Light" are other available options. -->

    <Application.DataTemplates>
        <local:ViewLocator/>
    </Application.DataTemplates>
  
    <Application.Styles>
        <FluentTheme />
		<Style Selector="TextBlock">
			<Setter Property="Background" Value="Bisque"/>
		</Style>
		<Style Selector="TextBlock.AnimatedTB">
			<Style.Animations>
				<Animation Duration="0:0:3" IterationCount="INFINITE" PlaybackDirection="Alternate" Easing="BounceEaseIn">
					<KeyFrame Cue="0%">
						<Setter Property="FontSize" Value="12"/>
					</KeyFrame>
					<KeyFrame Cue="100%">
						<Setter Property="FontSize" Value="48"/>
					</KeyFrame>
				</Animation>
			</Style.Animations>
		</Style>
    </Application.Styles>
</Application>