Ursa.Avalonia/src/Ursa.Themes.Semi/Controls/Form.axaml

<ResourceDictionary
    xmlns="https://github.com/avaloniaui"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:u="https://irihi.tech/ursa"
    xmlns:converters="clr-namespace:Ursa.Themes.Semi.Converters">
    <!--  Add Resources Here  -->
    <ControlTheme x:Key="{x:Type u:Form}"
                  TargetType="u:Form">
        <Setter Property="Grid.IsSharedSizeScope"
                Value="False" />
        <Setter Property="HorizontalAlignment" Value="Left" />
        <Setter Property="Template">
            <ControlTemplate TargetType="u:Form">
                <DataValidationErrors>
                    <ItemsPresenter
                        ItemsPanel="{TemplateBinding ItemsPanel}" />
                </DataValidationErrors>
            </ControlTemplate>
        </Setter>
        <Style Selector="^:fixed-width">
            <Setter Property="Grid.IsSharedSizeScope"
                    Value="True" />
        </Style>
    </ControlTheme>

    <ControlTheme x:Key="{x:Type u:FormGroup}"
                  TargetType="u:FormGroup">
        <Setter Property="Template">
            <ControlTemplate TargetType="u:FormGroup">
                <StackPanel>
                    <ContentPresenter
                        Margin="0,28,0,0"
                        Content="{TemplateBinding Header}"
                        FontSize="18"
                        FontWeight="{DynamicResource TextBlockTitleFontWeight}"
                        IsVisible="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=Header, Converter={x:Static ObjectConverters.IsNotNull}}" />
                    <Rectangle
                        Height="1"
                        Margin="0,8"
                        HorizontalAlignment="Stretch"
                        Fill="{DynamicResource FormGroupForeground}"
                        IsVisible="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=Header, Converter={x:Static ObjectConverters.IsNotNull}}" />
                    <ItemsPresenter
                        ItemsPanel="{TemplateBinding ItemsPanel}" />
                </StackPanel>
            </ControlTemplate>
        </Setter>
    </ControlTheme>

    <ControlTheme x:Key="{x:Type u:FormItem}"
                  TargetType="u:FormItem">
        <Setter Property="Margin" Value="0 8" />
        <Setter Property="Template">
            <ControlTemplate TargetType="u:FormItem">
                <StackPanel>
                    <StackPanel
                        Name="PART_LabelPanel"
                        Margin="0,0,0,4"
                        HorizontalAlignment="{TemplateBinding LabelAlignment}"
                        Orientation="Horizontal">
                        <Label
                            Name="PART_Label"
                            Content="{TemplateBinding Label}"
                            Background="Transparent"
                            FontWeight="{DynamicResource TextBlockTitleFontWeight}"
                            Target="{Binding #PART_ContentPresenter.Content}" />
                        <TextBlock
                            Foreground="{DynamicResource FormAsteriskForeground}"
                            IsVisible="{TemplateBinding IsRequired}"
                            Text="*" />
                    </StackPanel>
                    <ContentPresenter
                        Name="PART_ContentPresenter"
                        ContentTemplate="{TemplateBinding ContentTemplate}"
                        Content="{TemplateBinding Content}" />
                </StackPanel>
            </ControlTemplate>
        </Setter>
        <Style Selector="^:not(:no-label):horizontal">
            <Setter Property="Template">
                <ControlTemplate TargetType="u:FormItem">
                    <Grid RowDefinitions="*, *">
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="Auto"
                                SharedSizeGroup="Label" />
                            <ColumnDefinition Width="*" />
                        </Grid.ColumnDefinitions>
                        <Border
                            Grid.Row="0"
                            Grid.Column="0"
                            Width="{TemplateBinding LabelWidth}">
                            <StackPanel
                                Name="PART_LabelPanel"
                                Margin="{Binding #PART_Label.Bounds.Height, Converter={x:Static converters:FormContentHeightToMarginConverter.Instance}}"
                                HorizontalAlignment="{TemplateBinding LabelAlignment}"
                                VerticalAlignment="{Binding #PART_ContentPresenter.Bounds.Height, Converter={x:Static converters:FormContentHeightToAlignmentConverter.Instance}}"
                                Orientation="Horizontal">
                                <Label
                                    Name="PART_Label"
                                    Content="{TemplateBinding Label}"
                                    Background="Transparent"
                                    FontWeight="{DynamicResource TextBlockTitleFontWeight}"/>
                                <TextBlock
                                    Foreground="{DynamicResource FormAsteriskForeground}"
                                    IsVisible="{TemplateBinding IsRequired}"
                                    Text="*" />
                            </StackPanel>
                        </Border>
                        <ContentPresenter
                            Name="PART_ContentPresenter"
                            Grid.Row="0"
                            Grid.Column="1"
                            VerticalAlignment="Stretch"
                            VerticalContentAlignment="Center"
                            ContentTemplate="{TemplateBinding ContentTemplate}"
                            Content="{TemplateBinding Content}" />
                    </Grid>
                </ControlTemplate>
            </Setter>
        </Style>
        <Style Selector="^:no-label">
            <Setter Property="Template">
                <ControlTemplate TargetType="u:FormItem">
                    <ContentPresenter
                        ContentTemplate="{TemplateBinding ContentTemplate}"
                        Content="{TemplateBinding Content}" />
                </ControlTemplate>
            </Setter>
        </Style>
    </ControlTheme>
</ResourceDictionary>