Shaker/Avalonia/SukiUI/Theme/Expander.axaml

<ResourceDictionary xmlns="https://github.com/avaloniaui"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:content="clr-namespace:SukiUI.Content"
                    xmlns:controls="clr-namespace:SukiUI.Controls">
    <Design.PreviewWith>
        <Border Padding="20">
            <Expander Header="Expander" IsExpanded="True">
                <TextBlock Text="Content" />
            </Expander>
        </Border>
    </Design.PreviewWith>

    <ControlTheme x:Key="SukiExpanderStyle" TargetType="Expander">
        <Setter Property="TextBlock.TextAlignment" Value="Start" />
        <Setter Property="ClipToBounds" Value="False" />
        <Setter Property="CornerRadius" Value="4" />
        <Setter Property="ContentTransition" Value="{x:Null}" />
        <Setter Property="Template">
            <ControlTemplate>
                <Border Name="PART_RootBorder"
                        Background="{TemplateBinding Background}"
                        BorderBrush="{TemplateBinding BorderBrush}"
                        BorderThickness="{TemplateBinding BorderThickness}"
                        CornerRadius="{TemplateBinding CornerRadius}">
                    <Border Name="PART_InnerBorder" CornerRadius="{TemplateBinding CornerRadius}">
                        <Panel>
                            <controls:ContentExpandControl Name="PART_ContentExpand"
                                                           HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"
                                                           VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"
                                                           Content="{TemplateBinding Content}"
                                                           ContentTemplate="{TemplateBinding ContentTemplate}" />

                            <LayoutTransformControl Name="PART_ToggleTransform">
                                <DockPanel>
                                    <Border Name="PART_BottomBorder"
                                            Height="2"
                                            HorizontalAlignment="Stretch"
                                            Background="{DynamicResource SukiBorderBrush}"
                                            CornerRadius="10"
                                            DockPanel.Dock="Bottom"
                                            Opacity="0.8" />

                                    <ToggleButton Name="PART_ToggleButton"
                                                  HorizontalAlignment="Stretch"
                                                  VerticalAlignment="Center"
                                                  HorizontalContentAlignment="Stretch"
                                                  Background="Transparent"
                                                  BorderBrush="{DynamicResource SukiBorderBrush}"
                                                  BorderThickness="0"
                                                  Classes="Basic"
                                                  DockPanel.Dock="Right"
                                                  IsChecked="{TemplateBinding IsExpanded,
                                                                              Mode=TwoWay}">
                                        <Grid ColumnDefinitions="Auto,*,Auto">
                                            <ContentPresenter Grid.Column="0"
                                                              HorizontalAlignment="Left"
                                                              VerticalAlignment="Center"
                                                              Content="{TemplateBinding Header}"
                                                              FontWeight="{DynamicResource DefaultDemiBold}" />
                                            <PathIcon Name="PART_Icon"
                                                      Grid.Column="2"
                                                      Width="10"
                                                      Height="10"
                                                      Margin="10,0,0,0"
                                                      Data="{x:Static content:Icons.Plus}" />
                                        </Grid>
                                    </ToggleButton>
                                </DockPanel>
                            </LayoutTransformControl>
                        </Panel>
                    </Border>
                </Border>
            </ControlTemplate>
        </Setter>

        <Style Selector="^:not(.no-transitions) /template/ controls|ContentExpandControl#PART_ContentExpand">
            <Setter Property="Transitions">
                <Transitions>
                    <DoubleTransition Easing="CircularEaseOut"
                                      Property="Multiplier"
                                      Duration="0.25" />
                </Transitions>
            </Setter>
        </Style>

        <Style Selector="^ /template/ Border#PART_InnerBorder">
            <Setter Property="ClipToBounds" Value="True" />
        </Style>

        <Style Selector="^ /template/ LayoutTransformControl#PART_ToggleTransform">
            <Setter Property="ClipToBounds" Value="False" />
        </Style>

        <Style Selector="^ /template/ controls|ContentExpandControl#PART_ContentExpand">
            <Setter Property="Multiplier" Value="0" />
        </Style>

        <Style Selector="^:expanded /template/ controls|ContentExpandControl#PART_ContentExpand">
            <Setter Property="Multiplier" Value="1" />
        </Style>

        <Style Selector="^:expanded /template/ PathIcon#PART_Icon">
            <Setter Property="Data" Value="{x:Static content:Icons.Minus}" />
        </Style>

        <Style Selector="^:up">
            <Style Selector="^ /template/ controls|ContentExpandControl#PART_ContentExpand">
                <Setter Property="Orientation" Value="Vertical" />
                <Setter Property="VerticalAlignment" Value="Bottom" />
                <Setter Property="Margin" Value="0,0,0,48" />
            </Style>

            <Style Selector="^ /template/ LayoutTransformControl#PART_ToggleTransform">
                <Setter Property="VerticalAlignment" Value="Bottom" />
            </Style>

            <Style Selector="^ /template/ Border#PART_BottomBorder">
                <Setter Property="DockPanel.Dock" Value="Top" />
            </Style>
        </Style>

        <Style Selector="^:down">
            <Style Selector="^ /template/ controls|ContentExpandControl#PART_ContentExpand">
                <Setter Property="Orientation" Value="Vertical" />
                <Setter Property="VerticalAlignment" Value="Top" />
                <Setter Property="Margin" Value="0,48,0,0" />
            </Style>

            <Style Selector="^ /template/ LayoutTransformControl#PART_ToggleTransform">
                <Setter Property="VerticalAlignment" Value="Top" />
            </Style>
        </Style>

        <Style Selector="^:left">
            <Style Selector="^ /template/ controls|ContentExpandControl#PART_ContentExpand">
                <Setter Property="Orientation" Value="Horizontal" />
                <Setter Property="HorizontalAlignment" Value="Right" />
                <Setter Property="Margin" Value="0,0,48,0" />
            </Style>

            <Style Selector="^ /template/ LayoutTransformControl#PART_ToggleTransform">
                <Setter Property="LayoutTransform" Value="rotate(90deg)" />
                <Setter Property="HorizontalAlignment" Value="Right" />
            </Style>
        </Style>

        <Style Selector="^:right">
            <Style Selector="^ /template/ controls|ContentExpandControl#PART_ContentExpand">
                <Setter Property="Orientation" Value="Horizontal" />
                <Setter Property="HorizontalAlignment" Value="Left" />
                <Setter Property="Margin" Value="48,0,0,0" />
            </Style>

            <Style Selector="^ /template/ LayoutTransformControl#PART_ToggleTransform">
                <Setter Property="LayoutTransform" Value="rotate(90deg)" />
                <Setter Property="HorizontalAlignment" Value="Left" />
            </Style>

            <Style Selector="^ /template/ Border#PART_BottomBorder">
                <Setter Property="DockPanel.Dock" Value="Top" />
            </Style>
        </Style>
    </ControlTheme>

    <ControlTheme x:Key="{x:Type Expander}"
                  BasedOn="{StaticResource SukiExpanderStyle}"
                  TargetType="Expander" />
</ResourceDictionary>