Avalonia/src/Avalonia.Themes.Fluent/Controls/CheckBox.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="20">
        <CheckBox>Unchecked</CheckBox>
        <CheckBox IsChecked="True">Checked</CheckBox>
        <CheckBox IsThreeState="True" IsChecked="{x:Null}">Indeterminate</CheckBox>
        <CheckBox Width="120">Checkbox should wrap its text</CheckBox>
      </StackPanel>
    </Border>
  </Design.PreviewWith>

  <StreamGeometry x:Key="CheckMarkPathData">M5.5 10.586 1.707 6.793A1 1 0 0 0 .293 8.207l4.5 4.5a1 1 0 0 0 1.414 0l11-11A1 1 0 0 0 15.793.293L5.5 10.586Z</StreamGeometry>
  <x:Double x:Key="CheckBoxMinHeight">32</x:Double> 
  
  <ControlTheme x:Key="{x:Type CheckBox}" TargetType="CheckBox">
    <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="CornerRadius" Value="{DynamicResource ControlCornerRadius}" />
    <Setter Property="MinHeight" Value="{DynamicResource CheckBoxMinHeight}" />
    <Setter Property="Foreground" Value="{DynamicResource CheckBoxForegroundUnchecked}" />
    <Setter Property="Background" Value="{DynamicResource CheckBoxBackgroundUnchecked}" />
    <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxBorderBrushUnchecked}" />
    <Setter Property="Template">
      <ControlTemplate>
        <Grid x:Name="RootGrid" ColumnDefinitions="20,*">
          <Border x:Name="PART_Border"
                  Grid.ColumnSpan="2"
                  Background="{TemplateBinding Background}"
                  BorderBrush="{TemplateBinding BorderBrush}"
                  BorderThickness="{TemplateBinding BorderThickness}"
                  CornerRadius="{TemplateBinding CornerRadius}" />

          <Grid VerticalAlignment="Top" Height="{DynamicResource CheckBoxMinHeight}">
            <Border x:Name="NormalRectangle"
                    BorderBrush="{DynamicResource CheckBoxCheckBackgroundStrokeUnchecked}"
                    Background="{DynamicResource CheckBoxCheckBackgroundFillUnchecked}"
                    BorderThickness="{DynamicResource CheckBoxBorderThemeThickness}"
                    CornerRadius="{TemplateBinding CornerRadius}"
                    UseLayoutRounding="False"
                    Height="20"
                    Width="20" />

            <Viewbox UseLayoutRounding="False">
              <Panel>
                <Panel Height="16" Width="16" />
                <Path x:Name="CheckGlyph"
                      Opacity="0"
                      Fill="{DynamicResource CheckBoxCheckGlyphForegroundUnchecked}"
                      Stretch="Uniform"
                      VerticalAlignment="Center"
                      FlowDirection="LeftToRight" />
              </Panel>
            </Viewbox>
          </Grid>
          <ContentPresenter x:Name="PART_ContentPresenter"
                          ContentTemplate="{TemplateBinding ContentTemplate}"
                          Content="{TemplateBinding Content}"
                          Margin="{TemplateBinding Padding}"
                          HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                          VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                          TextWrapping="Wrap"
                          Grid.Column="1" />
        </Grid>
      </ControlTemplate>
    </Setter>

    <Style Selector="^ /template/ ContentPresenter#PART_ContentPresenter">
      <Setter Property="RecognizesAccessKey" Value="True" />
    </Style>

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

      <Style Selector="^ /template/ Border#PART_Border">
        <Setter Property="Background" Value="{DynamicResource CheckBoxBackgroundUncheckedPointerOver}" />
        <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxBorderBrushUncheckedPointerOver}" />
      </Style>

      <Style Selector="^ /template/ Border#NormalRectangle">
        <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxCheckBackgroundStrokeUncheckedPointerOver}" />
        <Setter Property="Background" Value="{DynamicResource CheckBoxCheckBackgroundFillUncheckedPointerOver}" />
      </Style>

      <Style Selector="^ /template/ Path#CheckGlyph">
        <Setter Property="Fill" Value="{DynamicResource CheckBoxCheckGlyphForegroundUncheckedPointerOver}" />
      </Style>
    </Style>

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

      <Style Selector="^ /template/ Border#PART_Border">
        <Setter Property="Background" Value="{DynamicResource CheckBoxBackgroundUncheckedPressed}" />
        <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxBorderBrushUncheckedPressed}" />
      </Style>

      <Style Selector="^ /template/ Border#NormalRectangle">
        <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxCheckBackgroundStrokeUncheckedPressed}" />
        <Setter Property="Background" Value="{DynamicResource CheckBoxCheckBackgroundFillUncheckedPressed}" />
      </Style>

      <Style Selector="^ /template/ Path#CheckGlyph">
        <Setter Property="Fill" Value="{DynamicResource CheckBoxCheckGlyphForegroundUncheckedPressed}" />
      </Style>
    </Style>

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

      <Style Selector="^ /template/ Border#PART_Border">
        <Setter Property="Background" Value="{DynamicResource CheckBoxBackgroundUncheckedDisabled}" />
        <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxBorderBrushUncheckedDisabled}" />
      </Style>

      <Style Selector="^ /template/ Border#NormalRectangle">
        <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxCheckBackgroundStrokeUncheckedDisabled}" />
        <Setter Property="Background" Value="{DynamicResource CheckBoxCheckBackgroundFillUncheckedDisabled}" />
      </Style>

      <Style Selector="^ /template/ Path#CheckGlyph">
        <Setter Property="Fill" Value="{DynamicResource CheckBoxCheckGlyphForegroundUncheckedDisabled}" />
      </Style>
    </Style>

    <Style Selector="^:checked">
      <!-- Checked Normal State -->
      <Setter Property="Foreground" Value="{DynamicResource CheckBoxForegroundChecked}" />
      <Setter Property="Background" Value="{DynamicResource CheckBoxBackgroundChecked}" />
      <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxBorderBrushChecked}" />

      <Style Selector="^ /template/ Border#NormalRectangle">
        <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxCheckBackgroundFillChecked}" />
        <Setter Property="Background" Value="{DynamicResource CheckBoxCheckBackgroundFillChecked}" />
      </Style>

      <Style Selector="^ /template/ Path#CheckGlyph">
        <Setter Property="Fill" Value="{DynamicResource CheckBoxCheckGlyphForegroundChecked}" />
        <Setter Property="Data" Value="{StaticResource CheckMarkPathData}" />
        <Setter Property="Width" Value="9" />
        <Setter Property="Opacity" Value="1" />
      </Style>

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

        <Style Selector="^ /template/ Border#PART_Border">
          <Setter Property="Background" Value="{DynamicResource CheckBoxBackgroundCheckedPointerOver}" />
          <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxBorderBrushCheckedPointerOver}" />
        </Style>

        <Style Selector="^ /template/ Border#NormalRectangle">
          <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxCheckBackgroundStrokeCheckedPointerOver}" />
          <Setter Property="Background" Value="{DynamicResource CheckBoxCheckBackgroundFillCheckedPointerOver}" />
        </Style>

        <Style Selector="^ /template/ Path#CheckGlyph">
          <Setter Property="Fill" Value="{DynamicResource CheckBoxCheckGlyphForegroundCheckedPointerOver}" />
        </Style>
      </Style>

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

        <Style Selector="^ /template/ Border#PART_Border">
          <Setter Property="Background" Value="{DynamicResource CheckBoxBackgroundCheckedPressed}" />
          <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxBorderBrushCheckedPressed}" />
        </Style>

        <Style Selector="^ /template/ Border#NormalRectangle">
          <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxCheckBackgroundStrokeCheckedPressed}" />
          <Setter Property="Background" Value="{DynamicResource CheckBoxCheckBackgroundFillCheckedPressed}" />
        </Style>

        <Style Selector="^ /template/ Path#CheckGlyph">
          <Setter Property="Fill" Value="{DynamicResource CheckBoxCheckGlyphForegroundCheckedPressed}" />
        </Style>
      </Style>

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

        <Style Selector="^ /template/ Border#PART_Border">
          <Setter Property="Background" Value="{DynamicResource CheckBoxBackgroundCheckedDisabled}" />
          <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxBorderBrushCheckedDisabled}" />
        </Style>

        <Style Selector="^ /template/ Border#NormalRectangle">
          <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxCheckBackgroundStrokeCheckedDisabled}" />
          <Setter Property="Background" Value="{DynamicResource CheckBoxCheckBackgroundFillCheckedDisabled}" />
        </Style>

        <Style Selector="^ /template/ Path#CheckGlyph">
          <Setter Property="Fill" Value="{DynamicResource CheckBoxCheckGlyphForegroundCheckedDisabled}" />
        </Style>
      </Style>
    </Style>

    <Style Selector="^:indeterminate">
      <!-- Indeterminate Normal State -->
      <Setter Property="Foreground" Value="{DynamicResource CheckBoxForegroundIndeterminate}" />
      <Setter Property="Background" Value="{DynamicResource CheckBoxBackgroundIndeterminate}" />
      <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxBorderBrushIndeterminate}" />

      <Style Selector="^ /template/ Border#NormalRectangle">
        <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxCheckBackgroundStrokeIndeterminate}" />
        <Setter Property="Background" Value="{DynamicResource CheckBoxCheckBackgroundFillIndeterminate}" />
      </Style>

      <Style Selector="^ /template/ Path#CheckGlyph">
        <Setter Property="Fill" Value="{DynamicResource CheckBoxCheckGlyphForegroundIndeterminate}" />
        <Setter Property="Data" Value="M1536 1536v-1024h-1024v1024h1024z" />
        <Setter Property="Width" Value="7" />
        <Setter Property="Opacity" Value="1" />
      </Style>

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

        <Style Selector="^ /template/ Border#PART_Border">
          <Setter Property="Background" Value="{DynamicResource CheckBoxBackgroundIndeterminatePointerOver}" />
          <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxBorderBrushIndeterminatePointerOver}" />
        </Style>

        <Style Selector="^ /template/ Border#NormalRectangle">
          <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxCheckBackgroundStrokeIndeterminatePointerOver}" />
          <Setter Property="Background" Value="{DynamicResource CheckBoxCheckBackgroundFillIndeterminatePointerOver}" />
        </Style>

        <Style Selector="^ /template/ Path#CheckGlyph">
          <Setter Property="Fill" Value="{DynamicResource CheckBoxCheckGlyphForegroundIndeterminatePointerOver}" />
        </Style>
      </Style>

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

        <Style Selector="^ /template/ Border#PART_Border">
          <Setter Property="Background" Value="{DynamicResource CheckBoxBackgroundIndeterminatePressed}" />
          <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxBorderBrushIndeterminatePressed}" />
        </Style>

        <Style Selector="^ /template/ Border#NormalRectangle">
          <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxCheckBackgroundStrokeIndeterminatePressed}" />
          <Setter Property="Background" Value="{DynamicResource CheckBoxCheckBackgroundFillIndeterminatePressed}" />
        </Style>

        <Style Selector="^ /template/ Path#CheckGlyph">
          <Setter Property="Fill" Value="{DynamicResource CheckBoxCheckGlyphForegroundIndeterminatePressed}" />
        </Style>
      </Style>

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

        <Style Selector="^ /template/ Border#PART_Border">
          <Setter Property="Background" Value="{DynamicResource CheckBoxBackgroundIndeterminateDisabled}" />
          <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxBorderBrushIndeterminateDisabled}" />
        </Style>

        <Style Selector="^ /template/ Border#NormalRectangle">
          <Setter Property="BorderBrush" Value="{DynamicResource CheckBoxCheckBackgroundStrokeIndeterminateDisabled}" />
          <Setter Property="Background" Value="{DynamicResource CheckBoxCheckBackgroundFillIndeterminateDisabled}" />
        </Style>

        <Style Selector="^ /template/ Path#CheckGlyph">
          <Setter Property="Fill" Value="{DynamicResource CheckBoxCheckGlyphForegroundIndeterminateDisabled}" />
        </Style>
      </Style>
    </Style>
  </ControlTheme>
</ResourceDictionary>