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

<ResourceDictionary xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    x:ClassModifier="internal">
  <Design.PreviewWith>
    <Border Padding="20">
      <StackPanel Spacing="10">
        <RadioButton Content="Option 1" Background="Green" />
        <RadioButton Content="Option 2" />
        <RadioButton IsEnabled="False" Content="Option 3" />
        <RadioButton Content="Option 2" />
      </StackPanel>
    </Border>
  </Design.PreviewWith>
  
  <ControlTheme x:Key="{x:Type RadioButton}" TargetType="RadioButton">
    <Setter Property="Background" Value="{DynamicResource RadioButtonBackground}" />
    <Setter Property="Foreground" Value="{DynamicResource RadioButtonForeground}" />
    <Setter Property="BorderBrush" Value="{DynamicResource RadioButtonBorderBrush}" />
    <Setter Property="CornerRadius" Value="{DynamicResource ControlCornerRadius}" />
    <Setter Property="Padding" Value="8,0,0,0" />
    <Setter Property="HorizontalAlignment" Value="Left" />
    <Setter Property="VerticalAlignment" Value="Center" />
    <Setter Property="HorizontalContentAlignment" Value="Left" />
    <Setter Property="VerticalContentAlignment" Value="Center" />
    <Setter Property="FontSize" Value="{DynamicResource ControlContentThemeFontSize}" />
    <Setter Property="Template">
      <ControlTemplate TargetType="RadioButton">
        <Border
            Name="RootBorder"
            Background="{TemplateBinding Background}"
            BorderBrush="{TemplateBinding BorderBrush}"
            BorderThickness="{TemplateBinding BorderThickness}"
            CornerRadius="{TemplateBinding CornerRadius}">
          <Grid ColumnDefinitions="20,*">
            <Grid Height="32" VerticalAlignment="Top">

              <Ellipse
                  Name="OuterEllipse"
                  Width="20"
                  Height="20"
                  Fill="{DynamicResource RadioButtonOuterEllipseFill}"
                  Stroke="{DynamicResource RadioButtonOuterEllipseStroke}"
                  StrokeThickness="{DynamicResource RadioButtonBorderThemeThickness}"
                  UseLayoutRounding="False" />

              <Ellipse
                  Name="CheckOuterEllipse"
                  Width="20"
                  Height="20"
                  Fill="{DynamicResource RadioButtonOuterEllipseCheckedFill}"
                  Opacity="0"
                  Stroke="{DynamicResource RadioButtonOuterEllipseCheckedStroke}"
                  StrokeThickness="{DynamicResource RadioButtonBorderThemeThickness}"
                  UseLayoutRounding="False" />

              <Ellipse
                  Name="CheckGlyph"
                  Width="8"
                  Height="8"
                  Fill="{DynamicResource RadioButtonCheckGlyphFill}"
                  Opacity="0"
                  Stroke="{DynamicResource RadioButtonCheckGlyphStroke}"
                  UseLayoutRounding="False" />
            </Grid>

            <ContentPresenter
                Name="PART_ContentPresenter"
                Grid.Column="1"
                Margin="{TemplateBinding Padding}"
                HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                Content="{TemplateBinding Content}"
                ContentTemplate="{TemplateBinding ContentTemplate}"
                Foreground="{TemplateBinding Foreground}"
                RecognizesAccessKey="True" />
          </Grid>
        </Border>
      </ControlTemplate>
    </Setter>

    <!--  PointerOver State  -->
    <Style Selector="^:pointerover /template/ ContentPresenter#PART_ContentPresenter">
      <Setter Property="Foreground" Value="{DynamicResource RadioButtonForegroundPointerOver}" />
    </Style>

    <Style Selector="^:pointerover /template/ Border#RootBorder">
      <Setter Property="Background" Value="{DynamicResource RadioButtonBackgroundPointerOver}" />
      <Setter Property="BorderBrush" Value="{DynamicResource RadioButtonBorderBrushPointerOver}" />
    </Style>

    <Style Selector="^:pointerover /template/ Ellipse#OuterEllipse">
      <Setter Property="Stroke" Value="{DynamicResource RadioButtonOuterEllipseStrokePointerOver}" />
      <Setter Property="Fill" Value="{DynamicResource RadioButtonOuterEllipseFillPointerOver}" />
    </Style>

    <Style Selector="^:pointerover /template/ Ellipse#CheckOuterEllipse">
      <Setter Property="Stroke" Value="{DynamicResource RadioButtonOuterEllipseCheckedStrokePointerOver}" />
      <Setter Property="Fill" Value="{DynamicResource RadioButtonOuterEllipseCheckedFillPointerOver}" />
    </Style>

    <Style Selector="^:pointerover /template/ Ellipse#CheckGlyph">
      <Setter Property="Stroke" Value="{DynamicResource RadioButtonCheckGlyphStrokePointerOver}" />
      <Setter Property="Fill" Value="{DynamicResource RadioButtonCheckGlyphFillPointerOver}" />
    </Style>


    <!--  Pressed State  -->
    <Style Selector="^:pressed /template/ ContentPresenter#PART_ContentPresenter">
      <Setter Property="Foreground" Value="{DynamicResource RadioButtonForegroundPressed}" />
    </Style>

    <Style Selector="^:pressed /template/ Border#RootBorder">
      <Setter Property="Background" Value="{DynamicResource RadioButtonBackgroundPressed}" />
      <Setter Property="BorderBrush" Value="{DynamicResource RadioButtonBorderBrushPressed}" />
    </Style>

    <Style Selector="^:pressed /template/ Ellipse#OuterEllipse">
      <Setter Property="Stroke" Value="{DynamicResource RadioButtonOuterEllipseStrokePressed}" />
      <Setter Property="Fill" Value="{DynamicResource RadioButtonOuterEllipseFillPressed}" />
    </Style>

    <Style Selector="^:pressed /template/ Ellipse#CheckOuterEllipse">
      <Setter Property="Stroke" Value="{DynamicResource RadioButtonOuterEllipseCheckedStrokePressed}" />
      <Setter Property="Fill" Value="{DynamicResource RadioButtonOuterEllipseCheckedFillPressed}" />
    </Style>

    <Style Selector="^:pressed /template/ Ellipse#CheckGlyph">
      <Setter Property="Stroke" Value="{DynamicResource RadioButtonCheckGlyphStrokePressed}" />
      <Setter Property="Fill" Value="{DynamicResource RadioButtonCheckGlyphFillPressed}" />
    </Style>


    <!--  Disabled State  -->
    <Style Selector="^:disabled /template/ ContentPresenter#PART_ContentPresenter">
      <Setter Property="Foreground" Value="{DynamicResource RadioButtonForegroundDisabled}" />
    </Style>

    <Style Selector="^:disabled /template/ Border#RootBorder">
      <Setter Property="Background" Value="{DynamicResource RadioButtonBackgroundDisabled}" />
      <Setter Property="BorderBrush" Value="{DynamicResource RadioButtonBorderBrushDisabled}" />
    </Style>

    <Style Selector="^:disabled /template/ Ellipse#OuterEllipse">
      <Setter Property="Stroke" Value="{DynamicResource RadioButtonOuterEllipseStrokeDisabled}" />
      <Setter Property="Fill" Value="{DynamicResource RadioButtonOuterEllipseFillDisabled}" />
    </Style>

    <Style Selector="^:disabled /template/ Ellipse#CheckOuterEllipse">
      <Setter Property="Stroke" Value="{DynamicResource RadioButtonOuterEllipseCheckedStrokeDisabled}" />
      <Setter Property="Fill" Value="{DynamicResource RadioButtonOuterEllipseCheckedFillDisabled}" />
    </Style>

    <Style Selector="^:disabled /template/ Ellipse#CheckGlyph">
      <Setter Property="Stroke" Value="{DynamicResource RadioButtonCheckGlyphFillDisabled}" />
      <Setter Property="Fill" Value="{DynamicResource RadioButtonCheckGlyphStrokeDisabled}" />
    </Style>


    <!--  Checked State  -->
    <Style Selector="^:checked /template/ Ellipse#CheckGlyph">
      <Setter Property="Opacity" Value="1" />
    </Style>

    <Style Selector="^:checked /template/ Ellipse#OuterEllipse">
      <Setter Property="Opacity" Value="0" />
    </Style>

    <Style Selector="^:checked /template/ Ellipse#CheckOuterEllipse">
      <Setter Property="Opacity" Value="1" />
    </Style>
  </ControlTheme>
</ResourceDictionary>