avalonia-practic/AvaloniaApplication5/Styles.axaml

<Styles xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
  <Design.PreviewWith>
    <Border Padding="20">
      <!-- Add Controls for Previewer Here -->
    </Border>
  </Design.PreviewWith>

	<Style Selector="Button">
		<Setter Property="Background" Value="DarkBlue"/>
		<Setter Property="Foreground" Value="White"/>
	</Style>
	<Style Selector="Button:pressed/template/ContentPresenter#PART_ContentPresenter">
		<Setter Property="Background" Value="BlueViolet"/>
	</Style>
	<Style Selector="Button:pointerover /template/ ContentPresenter#PART_ContentPresenter">
		<Setter Property="Background" Value="Blue"/>
		<Setter Property="Foreground" Value="White"/>
	</Style>
	<Style Selector="ComboBox:pointerover /template/ Border#Background">
		<Setter Property="Background" Value="Blue"/>
		<Setter Property="BorderBrush" Value="LightBlue" />
	</Style>
	<Style Selector="DatePicker">
		<Setter Property="Foreground" Value="White"/>
	</Style>

	<Style Selector="TextBlock">
		<Setter Property="Foreground" Value="DarkBlue"/>
		<Setter Property="FontSize" Value="16"/>
	</Style>
	<!-- Add Styles Here -->
</Styles>