Avalonia/src/Avalonia.Themes.Fluent/Controls/Button.xaml

<Styles xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
  <Design.PreviewWith>
    <Border Padding="20">
      <StackPanel Spacing="20">
        <Button Content="Click Me!" />
        <Button Classes="accent" Content="Click Me!" />
      </StackPanel>      
    </Border>
  </Design.PreviewWith>
  <Styles.Resources>
    <Thickness x:Key="ButtonPadding">8,5,8,6</Thickness>
  </Styles.Resources>
  <Style Selector="Button">
    <Setter Property="Background" Value="{DynamicResource ButtonBackground}" />
    <!--<Setter Property="BackgroundSizing" Value="OuterBorderEdge" />-->
    <Setter Property="Foreground" Value="{DynamicResource ButtonForeground}" />
    <Setter Property="BorderBrush" Value="{DynamicResource ButtonBorderBrush}" />
    <Setter Property="BorderThickness" Value="{DynamicResource ButtonBorderThemeThickness}" />
    <Setter Property="Padding" Value="{DynamicResource ButtonPadding}" />
    <Setter Property="HorizontalAlignment" Value="Left" />
    <Setter Property="VerticalAlignment" Value="Center" />    
    <Setter Property="FontWeight" Value="Normal" />
    <Setter Property="FontSize" Value="{DynamicResource ControlContentThemeFontSize}" />
    <!--<Setter Property="UseSystemFocusVisuals" Value="{StaticResource UseSystemFocusVisuals}" />
    <Setter Property="FocusVisualMargin" Value="-3" />-->
    <Setter Property="Template">
      <ControlTemplate>
        <ContentPresenter x:Name="PART_ContentPresenter"
                          Background="{TemplateBinding Background}"
                          BorderBrush="{TemplateBinding BorderBrush}"
                          BorderThickness="{TemplateBinding BorderThickness}"
                          Content="{TemplateBinding Content}"
                          ContentTemplate="{TemplateBinding ContentTemplate}"
                          Padding="{TemplateBinding Padding}"
                          HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"
                          VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}" />
      </ControlTemplate>
    </Setter>
  </Style>

  <!-- PointerOverState -->  
  <Style Selector="Button:pointerover /template/ ContentPresenter#PART_ContentPresenter">
    <Setter Property="Background" Value="{DynamicResource ButtonBackgroundPointerOver}" />
    <Setter Property="BorderBrush" Value="{DynamicResource ButtonBorderBrushPointerOver}" />
    <Setter Property="TextBlock.Foreground" Value="{DynamicResource ButtonForegroundPointerOver}" />
  </Style>
  
  <Style Selector="Button:pressed  /template/ ContentPresenter#PART_ContentPresenter">
    <Setter Property="Background" Value="{DynamicResource ButtonBackgroundPressed}" />
    <Setter Property="BorderBrush" Value="{DynamicResource ButtonBorderBrushPressed}" />
    <Setter Property="TextBlock.Foreground" Value="{DynamicResource ButtonForegroundPressed}" />
  </Style>
  
  <Style Selector="Button:disabled /template/ ContentPresenter#PART_ContentPresenter">
    <Setter Property="Background" Value="{DynamicResource ButtonBackgroundDisabled}" />
    <Setter Property="BorderBrush" Value="{DynamicResource ButtonBorderBrushDisabled}" />
    <Setter Property="TextBlock.Foreground" Value="{DynamicResource ButtonForegroundDisabled}" />
  </Style>

  <Style Selector="Button.accent /template/ ContentPresenter#PART_ContentPresenter">
    <Setter Property="Background" Value="{DynamicResource AccentButtonBackground}" />
    <Setter Property="BorderBrush" Value="{DynamicResource AccentButtonBorderBrush}" />
    <Setter Property="TextBlock.Foreground" Value="{DynamicResource AccentButtonForeground}" />
  </Style>

  <Style Selector="Button.accent:pointerover /template/ ContentPresenter#PART_ContentPresenter">
    <Setter Property="Background" Value="{DynamicResource AccentButtonBackgroundPointerOver}" />
    <Setter Property="BorderBrush" Value="{DynamicResource AccentButtonBorderBrushPointerOver}" />
    <Setter Property="TextBlock.Foreground" Value="{DynamicResource AccentButtonForegroundPointerOver}" />
  </Style>

  <Style Selector="Button.accent:pressed  /template/ ContentPresenter#PART_ContentPresenter">
    <Setter Property="Background" Value="{DynamicResource AccentButtonBackgroundPressed}" />
    <Setter Property="BorderBrush" Value="{DynamicResource AccentButtonBorderBrushPressed}" />
    <Setter Property="TextBlock.Foreground" Value="{DynamicResource AccentButtonForegroundPressed}" />
  </Style>

  <Style Selector="Button, RepeatButton, ToggleButton">
    <Setter Property="RenderTransform" Value="none" />
    <Setter Property="Transitions">
      <Transitions>
        <TransformOperationsTransition Property="RenderTransform" Duration="0:0:.075" />
      </Transitions>
    </Setter>
  </Style>

  <Style Selector="Button:pressed, RepeatButton:pressed, ToggleButton:pressed">
    <Setter Property="RenderTransform" Value="scale(0.98)" />    
  </Style>

  <Style Selector="Button.accent:disabled /template/ ContentPresenter#PART_ContentPresenter">
    <Setter Property="Background" Value="{DynamicResource AccentButtonBackgroundDisabled}" />
    <Setter Property="BorderBrush" Value="{DynamicResource AccentButtonBorderBrushDisabled}" />
    <Setter Property="TextBlock.Foreground" Value="{DynamicResource AccentButtonForegroundDisabled}" />
  </Style>
  
  <Style Selector="Button /template/ ContentPresenter#PART_ContentPresenter">
    <Setter Property="CornerRadius" Value="{DynamicResource ControlCornerRadius}" />
  </Style>
</Styles>