diff --git a/Minint/ViewModels/EditorViewModel.cs b/Minint/ViewModels/EditorViewModel.cs
index b0f1ca0..3472126 100644
--- a/Minint/ViewModels/EditorViewModel.cs
+++ b/Minint/ViewModels/EditorViewModel.cs
@@ -640,6 +640,8 @@ public partial class EditorViewModel : ViewModelBase
         _animationTimer?.Stop();
         _animationTimer = null;
         IsPlaying = false;
+        if (ActiveDocument is not null)
+            SyncLayersAndCanvas(ActiveDocument);
     }
 
     private void AdvanceAnimationFrame()
diff --git a/Minint/ViewModels/MainWindowViewModel.cs b/Minint/ViewModels/MainWindowViewModel.cs
index 769933b..5251e7c 100644
--- a/Minint/ViewModels/MainWindowViewModel.cs
+++ b/Minint/ViewModels/MainWindowViewModel.cs
@@ -50,10 +50,18 @@ public partial class MainWindowViewModel : ViewModelBase
     #region File commands
 
     [RelayCommand]
-    private void NewFile()
+    private async Task NewFileAsync()
     {
-        Editor.NewContainer(64, 64);
-        StatusText = "New 64×64 container created.";
+        if (Owner is not Window window) return;
+
+        var dialog = new NewContainerDialog();
+        var result = await dialog.ShowDialog<bool?>(window);
+        if (result != true) return;
+
+        int w = dialog.CanvasWidth;
+        int h = dialog.CanvasHeight;
+        Editor.NewContainer(w, h);
+        StatusText = $"New {w}×{h} container created.";
     }
 
     [RelayCommand]
diff --git a/Minint/Views/NewContainerDialog.axaml b/Minint/Views/NewContainerDialog.axaml
new file mode 100644
index 0000000..bf7762a
--- /dev/null
+++ b/Minint/Views/NewContainerDialog.axaml
@@ -0,0 +1,31 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        x:Class="Minint.Views.NewContainerDialog"
+        Title="New Container"
+        Width="300"
+        WindowStartupLocation="CenterOwner"
+        CanResize="False"
+        SizeToContent="Height">
+    <StackPanel Margin="16" Spacing="12">
+        <TextBlock Text="Canvas size:" FontWeight="SemiBold"/>
+
+        <Grid ColumnDefinitions="Auto,*" RowDefinitions="Auto,Auto" RowSpacing="8" ColumnSpacing="8">
+            <TextBlock Grid.Row="0" Grid.Column="0" Text="Width:" VerticalAlignment="Center"/>
+            <NumericUpDown Grid.Row="0" Grid.Column="1"
+                           x:Name="WidthInput"
+                           Value="64" Minimum="1" Maximum="4096" Increment="1"
+                           FormatString="0"/>
+
+            <TextBlock Grid.Row="1" Grid.Column="0" Text="Height:" VerticalAlignment="Center"/>
+            <NumericUpDown Grid.Row="1" Grid.Column="1"
+                           x:Name="HeightInput"
+                           Value="64" Minimum="1" Maximum="4096" Increment="1"
+                           FormatString="0"/>
+        </Grid>
+
+        <StackPanel Orientation="Horizontal" HorizontalAlignment="Right" Spacing="8" Margin="0,8,0,0">
+            <Button Content="Create" x:Name="OkButton" IsDefault="True" Padding="16,6"/>
+            <Button Content="Cancel" x:Name="CancelButton" IsCancel="True" Padding="16,6"/>
+        </StackPanel>
+    </StackPanel>
+</Window>
diff --git a/Minint/Views/NewContainerDialog.axaml.cs b/Minint/Views/NewContainerDialog.axaml.cs
new file mode 100644
index 0000000..dddaab5
--- /dev/null
+++ b/Minint/Views/NewContainerDialog.axaml.cs
@@ -0,0 +1,17 @@
+using Avalonia.Controls;
+
+namespace Minint.Views;
+
+public partial class NewContainerDialog : Window
+{
+    public int CanvasWidth => (int)(WidthInput.Value ?? 64);
+    public int CanvasHeight => (int)(HeightInput.Value ?? 64);
+
+    public NewContainerDialog()
+    {
+        InitializeComponent();
+
+        OkButton.Click += (_, _) => Close(true);
+        CancelButton.Click += (_, _) => Close(false);
+    }
+}
diff --git a/Minint/Views/PatternDialog.axaml b/Minint/Views/PatternDialog.axaml
index 376e722..8b82d8c 100644
--- a/Minint/Views/PatternDialog.axaml
+++ b/Minint/Views/PatternDialog.axaml
@@ -2,10 +2,12 @@
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         x:Class="Minint.Views.PatternDialog"
         Title="Generate Pattern"
-        Width="360"
+        Width="640"
+        Height="520"
+        MinWidth="480"
+        MinHeight="400"
         WindowStartupLocation="CenterOwner"
-        CanResize="False"
-        SizeToContent="Height">
+        CanResize="True">
     <StackPanel Margin="16" Spacing="8">
         <Grid ColumnDefinitions="100,*" RowDefinitions="Auto,Auto,Auto,Auto,Auto,Auto" RowSpacing="6" ColumnSpacing="8">
             <TextBlock Grid.Row="0" Grid.Column="0" Text="Pattern:" VerticalAlignment="Center"/>