Minint/Minint/Views/MainWindow.axaml

<Window xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:vm="using:Minint.ViewModels"
        xmlns:controls="using:Minint.Controls"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d" d:DesignWidth="1024" d:DesignHeight="700"
        x:Class="Minint.Views.MainWindow"
        x:DataType="vm:MainWindowViewModel"
        Icon="/Assets/avalonia-logo.ico"
        Title="{Binding Editor.Title}"
        Width="1024" Height="700">

    <Design.DataContext>
        <vm:MainWindowViewModel/>
    </Design.DataContext>

    <DockPanel>
        <!-- Menu bar -->
        <Menu DockPanel.Dock="Top">
            <MenuItem Header="_File">
                <MenuItem Header="_New" Command="{Binding NewFileCommand}" HotKey="Ctrl+N"/>
                <MenuItem Header="_Open…" Command="{Binding OpenFileCommand}" HotKey="Ctrl+O"/>
                <Separator/>
                <MenuItem Header="_Save" Command="{Binding SaveFileCommand}" HotKey="Ctrl+S"/>
                <MenuItem Header="Save _As…" Command="{Binding SaveFileAsCommand}" HotKey="Ctrl+Shift+S"/>
            </MenuItem>
            <MenuItem Header="_View">
                <MenuItem Header="Pixel _Grid" ToggleType="CheckBox"
                          IsChecked="{Binding Editor.ShowGrid}" HotKey="Ctrl+G"/>
            </MenuItem>
        </Menu>

        <!-- Toolbar -->
        <Border DockPanel.Dock="Top"
                BorderBrush="{DynamicResource SystemControlForegroundBaseMediumLowBrush}"
                BorderThickness="0,0,0,1" Padding="6,4">
            <StackPanel Orientation="Horizontal" Spacing="10">
                <RadioButton GroupName="Tool" Content="Brush"
                             ToolTip.Tip="Brush tool — draw with selected color"
                             IsChecked="{Binding Editor.ActiveTool, Converter={x:Static vm:ToolTypeConverters.IsBrush}}"
                             Command="{Binding Editor.SelectBrushCommand}"/>
                <RadioButton GroupName="Tool" Content="Eraser"
                             ToolTip.Tip="Eraser tool — erase to transparent"
                             IsChecked="{Binding Editor.ActiveTool, Converter={x:Static vm:ToolTypeConverters.IsEraser}}"
                             Command="{Binding Editor.SelectEraserCommand}"/>
                <RadioButton GroupName="Tool" Content="Fill"
                             ToolTip.Tip="Fill tool — flood fill with selected color"
                             IsChecked="{Binding Editor.ActiveTool, Converter={x:Static vm:ToolTypeConverters.IsFill}}"
                             Command="{Binding Editor.SelectFillCommand}"/>

                <Separator/>

                <TextBlock Text="Size:" VerticalAlignment="Center"/>
                <Slider Value="{Binding Editor.BrushRadius}" Minimum="0" Maximum="64"
                        TickFrequency="1" IsSnapToTickEnabled="True" Width="120"
                        VerticalAlignment="Center"/>
                <TextBlock Text="{Binding Editor.BrushRadius}" VerticalAlignment="Center"
                           Width="20" TextAlignment="Center"/>

                <Separator/>

                <TextBlock Text="Color:" VerticalAlignment="Center"/>
                <ColorPicker x:Name="ToolColorPicker"
                             Color="{Binding Editor.PreviewColor, Mode=TwoWay}"
                             IsAlphaVisible="False"
                             VerticalAlignment="Center"/>
            </StackPanel>
        </Border>

        <!-- Status bar -->
        <Border DockPanel.Dock="Bottom" Background="{DynamicResource SystemControlBackgroundChromeMediumLowBrush}"
                Padding="8,2">
            <TextBlock Text="{Binding StatusText}" FontSize="12"/>
        </Border>

        <!-- Main content: left panel, canvas, right panel -->
        <Grid ColumnDefinitions="200,*,200">

            <!-- Left panel: documents -->
            <Border Grid.Column="0" BorderBrush="{DynamicResource SystemControlForegroundBaseMediumLowBrush}"
                    BorderThickness="0,0,1,0" Padding="4">
                <DockPanel>
                    <TextBlock DockPanel.Dock="Top" Text="Documents" FontWeight="SemiBold" Margin="0,0,0,4"/>
                    <StackPanel DockPanel.Dock="Bottom" Orientation="Horizontal" Spacing="2" Margin="0,4,0,0">
                        <Button Content="+" ToolTip.Tip="Add document"
                                Command="{Binding Editor.AddDocumentCommand}" Padding="6,2"/>
                        <Button Content="−" ToolTip.Tip="Remove document"
                                Command="{Binding Editor.RemoveDocumentCommand}" Padding="6,2"/>
                        <Button Content="▲" ToolTip.Tip="Move up"
                                Command="{Binding Editor.MoveDocumentUpCommand}" Padding="6,2"/>
                        <Button Content="▼" ToolTip.Tip="Move down"
                                Command="{Binding Editor.MoveDocumentDownCommand}" Padding="6,2"/>
                    </StackPanel>
                    <ListBox ItemsSource="{Binding Editor.Documents}"
                             SelectedItem="{Binding Editor.ActiveDocument}"
                             SelectionMode="Single">
                        <ListBox.ItemTemplate>
                            <DataTemplate>
                                <controls:EditableTextBlock Text="{Binding Name}"/>
                            </DataTemplate>
                        </ListBox.ItemTemplate>
                    </ListBox>
                </DockPanel>
            </Border>

            <!-- Center: canvas with scrollbars -->
            <Grid Grid.Column="1" RowDefinitions="*,Auto" ColumnDefinitions="*,Auto">
                <Border Grid.Row="0" Grid.Column="0" Background="#FF1E1E1E" ClipToBounds="True">
                    <controls:PixelCanvas x:Name="Canvas"
                                           SourceBitmap="{Binding Editor.CanvasBitmap}"
                                           ShowGrid="{Binding Editor.ShowGrid}"/>
                </Border>
                <ScrollBar x:Name="HScroll" Grid.Row="1" Grid.Column="0"
                           Orientation="Horizontal"/>
                <ScrollBar x:Name="VScroll" Grid.Row="0" Grid.Column="1"
                           Orientation="Vertical"/>
            </Grid>

            <!-- Right panel: layers -->
            <Border Grid.Column="2" BorderBrush="{DynamicResource SystemControlForegroundBaseMediumLowBrush}"
                    BorderThickness="1,0,0,0" Padding="4">
                <DockPanel>
                    <TextBlock DockPanel.Dock="Top" Text="Layers" FontWeight="SemiBold" Margin="0,0,0,4"/>
                    <StackPanel DockPanel.Dock="Bottom" Orientation="Horizontal" Spacing="2" Margin="0,4,0,0">
                        <Button Content="+" ToolTip.Tip="Add layer"
                                Command="{Binding Editor.AddLayerCommand}" Padding="6,2"/>
                        <Button Content="−" ToolTip.Tip="Remove layer"
                                Command="{Binding Editor.RemoveLayerCommand}" Padding="6,2"/>
                        <Button Content="▲" ToolTip.Tip="Move up"
                                Command="{Binding Editor.MoveLayerUpCommand}" Padding="6,2"/>
                        <Button Content="▼" ToolTip.Tip="Move down"
                                Command="{Binding Editor.MoveLayerDownCommand}" Padding="6,2"/>
                        <Button Content="⧉" ToolTip.Tip="Duplicate layer"
                                Command="{Binding Editor.DuplicateLayerCommand}" Padding="6,2"/>
                    </StackPanel>
                    <ListBox ItemsSource="{Binding Editor.Layers}"
                             SelectedItem="{Binding Editor.ActiveLayer}"
                             SelectionMode="Single">
                        <ListBox.ItemTemplate>
                            <DataTemplate>
                                <StackPanel Orientation="Horizontal" Spacing="4">
                                    <CheckBox IsChecked="{Binding IsVisible}" MinWidth="0"
                                              VerticalAlignment="Center"
                                              ToolTip.Tip="Toggle layer visibility"/>
                                    <controls:EditableTextBlock Text="{Binding Name}"
                                             VerticalAlignment="Center" MinWidth="60"/>
                                </StackPanel>
                            </DataTemplate>
                        </ListBox.ItemTemplate>
                    </ListBox>
                </DockPanel>
            </Border>

        </Grid>
    </DockPanel>
</Window>