Styles: add shared Typography/Scroll resources; add platform overrides (Desktop/Android/Browser) and load via App; switch icons to resource-based sizes and cap history text lines.

src/AdvancedCalculator.Android/Styles/Android.axaml

@@ -0,0 +1,17 @@
+<ResourceDictionary xmlns="https://github.com/avaloniaui"
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+  <!-- Android overrides: larger, touch-first -->
+  <x:Double x:Key="FontSizeBase">16</x:Double>
+  <x:Double x:Key="FontSizeLarge">18</x:Double>
+  <x:Double x:Key="IconSizeM">24</x:Double>
+  <x:Double x:Key="LineHeightBase">1.35</x:Double>
+
+  <!-- Thin overlay-like scrollbars -->
+  <Style Selector="ScrollBar:vertical">
+    <Setter Property="Width" Value="8"/>
+  </Style>
+  <Style Selector="ScrollBar:horizontal">
+    <Setter Property="Height" Value="8"/>
+  </Style>
+</ResourceDictionary>
+

src/AdvancedCalculator.Browser/Styles/Browser.axaml

@@ -0,0 +1,16 @@
+<ResourceDictionary xmlns="https://github.com/avaloniaui"
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+  <!-- Browser overrides: middle ground -->
+  <x:Double x:Key="FontSizeBase">15</x:Double>
+  <x:Double x:Key="IconSizeM">22</x:Double>
+  <x:Double x:Key="LineHeightBase">1.3</x:Double>
+
+  <!-- Slightly thinner scrollbars on web -->
+  <Style Selector="ScrollBar:vertical">
+    <Setter Property="Width" Value="8"/>
+  </Style>
+  <Style Selector="ScrollBar:horizontal">
+    <Setter Property="Height" Value="8"/>
+  </Style>
+</ResourceDictionary>
+

src/AdvancedCalculator.Desktop/Styles/Desktop.axaml

@@ -0,0 +1,16 @@
+<ResourceDictionary xmlns="https://github.com/avaloniaui"
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+  <!-- Desktop overrides: slightly denser -->
+  <x:Double x:Key="FontSizeBase">13</x:Double>
+  <x:Double x:Key="LineHeightBase">1.2</x:Double>
+  <x:Double x:Key="IconSizeM">20</x:Double>
+
+  <!-- Scrollbars a bit thicker on desktop -->
+  <Style Selector="ScrollBar:vertical">
+    <Setter Property="Width" Value="12"/>
+  </Style>
+  <Style Selector="ScrollBar:horizontal">
+    <Setter Property="Height" Value="12"/>
+  </Style>
+</ResourceDictionary>
+

src/AdvancedCalculator/App.axaml

@@ -6,6 +6,8 @@
 
     <Application.Styles>
         <FluentTheme />
+        <StyleInclude Source="avares://AdvancedCalculator/Styles/Typography.axaml"/>
+        <StyleInclude Source="avares://AdvancedCalculator/Styles/Scroll.axaml"/>
     </Application.Styles>
 
     <Application.Resources>

src/AdvancedCalculator/App.axaml.cs

@@ -5,6 +5,8 @@ using Avalonia;
 using Avalonia.Controls.ApplicationLifetimes;
 using Avalonia.Data.Core.Plugins;
 using Avalonia.Markup.Xaml;
+using Avalonia.Styling;
+using System;
 
 namespace AdvancedCalculator;
 
@@ -21,6 +23,40 @@ public partial class App : Application
         // Without this line you will get duplicate validations from both Avalonia and CT
         BindingPlugins.DataValidators.RemoveAt(0);
 
+        // Load platform-specific styles (typography, scrollbars overrides)
+        try
+        {
+            var styles = Current?.Styles;
+            if (styles is not null)
+            {
+                if (OperatingSystem.IsAndroid())
+                {
+                    styles.Add(new StyleInclude(new Uri("avares://AdvancedCalculator/"))
+                    {
+                        Source = new Uri("avares://AdvancedCalculator.Android/Styles/Android.axaml")
+                    });
+                }
+                else if (OperatingSystem.IsBrowser())
+                {
+                    styles.Add(new StyleInclude(new Uri("avares://AdvancedCalculator/"))
+                    {
+                        Source = new Uri("avares://AdvancedCalculator.Browser/Styles/Browser.axaml")
+                    });
+                }
+                else
+                {
+                    styles.Add(new StyleInclude(new Uri("avares://AdvancedCalculator/"))
+                    {
+                        Source = new Uri("avares://AdvancedCalculator.Desktop/Styles/Desktop.axaml")
+                    });
+                }
+            }
+        }
+        catch
+        {
+            // If a platform-specific style dictionary is missing, continue without failing.
+        }
+
         if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
         {
             desktop.MainWindow = new MainWindow

src/AdvancedCalculator/Converters/WidthToBooleanConverter.cs

@@ -0,0 +1,31 @@
+using System;
+using System.Globalization;
+using Avalonia.Data.Converters;
+
+namespace AdvancedCalculator.Converters;
+
+// Returns true if width (double) is less than the provided threshold (parameter),
+// otherwise false. Default threshold is 640 when parameter is null or invalid.
+public class WidthToBooleanConverter : IValueConverter
+{
+    public static readonly WidthToBooleanConverter Instance = new();
+
+    public object? Convert(object? value, Type targetType, object? parameter, CultureInfo? culture)
+    {
+        if (value is double width)
+        {
+            double threshold = 640;
+            if (parameter is double p)
+                threshold = p;
+            else if (parameter is string s && double.TryParse(s, NumberStyles.Number, CultureInfo.InvariantCulture, out var parsed))
+                threshold = parsed;
+
+            return width < threshold;
+        }
+        return false;
+    }
+
+    public object? ConvertBack(object? value, Type targetType, object? parameter, CultureInfo? culture)
+        => throw new NotSupportedException();
+}
+

src/AdvancedCalculator/Styles/Scroll.axaml

@@ -0,0 +1,21 @@
+<ResourceDictionary xmlns="https://github.com/avaloniaui"
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+  <!-- Shared scrolling defaults -->
+  <Style Selector="ListBox">
+    <Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Auto"/>
+    <Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Disabled"/>
+  </Style>
+
+  <Style Selector="ScrollViewer">
+    <Setter Property="CanScrollHorizontally" Value="False"/>
+  </Style>
+
+  <!-- Thin-ish scrollbars by default; platform overrides will adjust -->
+  <Style Selector="ScrollBar:vertical">
+    <Setter Property="Width" Value="10"/>
+  </Style>
+  <Style Selector="ScrollBar:horizontal">
+    <Setter Property="Height" Value="10"/>
+  </Style>
+</ResourceDictionary>
+

src/AdvancedCalculator/Styles/Typography.axaml

@@ -0,0 +1,30 @@
+<ResourceDictionary xmlns="https://github.com/avaloniaui"
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+  <!-- Shared typography resources -->
+  <x:Double x:Key="FontSizeSmall">12</x:Double>
+  <x:Double x:Key="FontSizeBase">14</x:Double>
+  <x:Double x:Key="FontSizeLarge">16</x:Double>
+  <x:Double x:Key="FontSizeXL">20</x:Double>
+
+  <x:Double x:Key="IconSizeS">18</x:Double>
+  <x:Double x:Key="IconSizeM">22</x:Double>
+  <x:Double x:Key="IconSizeL">26</x:Double>
+
+  <x:Double x:Key="LineHeightTight">1.1</x:Double>
+  <x:Double x:Key="LineHeightBase">1.25</x:Double>
+  <x:Double x:Key="LineHeightRelaxed">1.4</x:Double>
+
+  <!-- Defaults for text -->
+  <Style Selector="TextBlock">
+    <Setter Property="TextElement.FontSize" Value="{DynamicResource FontSizeBase}"/>
+    <Setter Property="TextWrapping" Value="Wrap"/>
+    <Setter Property="LineHeight" Value="{DynamicResource LineHeightBase}"/>
+  </Style>
+
+  <!-- Subtle caption text helper -->
+  <Style Selector="TextBlock.caption">
+    <Setter Property="TextElement.FontSize" Value="{DynamicResource FontSizeSmall}"/>
+    <Setter Property="Opacity" Value="0.85"/>
+  </Style>
+</ResourceDictionary>
+

src/AdvancedCalculator/ViewModels/MainViewModel.cs

@@ -41,6 +41,37 @@ public partial class MainViewModel : ViewModelBase
         IsFunctionsPanelOpen = !IsFunctionsPanelOpen;
     }
 
+    // Insert helpers for touch: appends tokens to the input box
+    [RelayCommand]
+    private void InsertVariable(string? variableName)
+    {
+        if (string.IsNullOrWhiteSpace(variableName))
+            return;
+        InsertToken(variableName);
+    }
+
+    [RelayCommand]
+    private void InsertFunction(string? functionName)
+    {
+        if (string.IsNullOrWhiteSpace(functionName))
+            return;
+        InsertToken(functionName + "()");
+    }
+
+    private void InsertToken(string token)
+    {
+        if (string.IsNullOrEmpty(InputText))
+        {
+            InputText = token;
+            return;
+        }
+
+        if (!char.IsWhiteSpace(InputText[^1]))
+            InputText += " ";
+
+        InputText += token;
+    }
+
     [RelayCommand(AllowConcurrentExecutions = false)]
     private async Task Submit()
     {

src/AdvancedCalculator/Views/MainView.axaml

@@ -10,40 +10,96 @@
              x:DataType="vm:MainViewModel">
   <UserControl.Resources>
     <conv:BoolToGridLengthConverter x:Key="BoolToGridLengthConverter" />
+    <conv:WidthToBooleanConverter x:Key="WidthToBooleanConverter" />
   </UserControl.Resources>
+  <!-- Replace columns with a responsive SplitView -->
+  <SplitView x:Name="RootSplit"
+             OpenPaneLength="320"
+             CompactPaneLength="0">
+    <!-- Responsive behavior: set DisplayMode and IsPaneOpen based on width -->
+    <SplitView.Styles>
+      <Style Selector="SplitView#RootSplit">
+        <Style.Triggers>
+          <!-- Narrow: Overlay mode, pane closed by default -->
+          <DataTrigger Value="True"
+                       Binding="{Binding $parent[Window].Bounds.Width,
+                                         Converter={StaticResource WidthToBooleanConverter},
+                                         ConverterParameter=640}">
+            <Setter Property="DisplayMode" Value="Overlay" />
+            <Setter Property="IsPaneOpen" Value="False" />
+          </DataTrigger>
+          <!-- Wide: Inline mode, pane open -->
+          <DataTrigger Value="False"
+                       Binding="{Binding $parent[Window].Bounds.Width,
+                                         Converter={StaticResource WidthToBooleanConverter},
+                                         ConverterParameter=640}">
+            <Setter Property="DisplayMode" Value="Inline" />
+            <Setter Property="IsPaneOpen" Value="True" />
+          </DataTrigger>
+        </Style.Triggers>
+      </Style>
+    </SplitView.Styles>
 
-  <Grid ColumnDefinitions="*,3*">
-    <!-- Left column: Variables + Functions -->
-    <Grid Grid.Column="0">
+    <!-- Left pane: Variables + Functions -->
+    <SplitView.Pane>
+      <Grid>
         <Grid.RowDefinitions>
           <RowDefinition Height="*" />
           <RowDefinition Height="{Binding IsFunctionsPanelOpen, Converter={StaticResource BoolToGridLengthConverter}}" />
         </Grid.RowDefinitions>
 
-      <!-- Variables list -->
-      <ListBox Grid.Row="0" ItemsSource="{Binding Variables}" SelectedIndex="-1">
+        <!-- Variables list with empty-state hint overlay -->
+        <Grid Grid.Row="0">
+          <ListBox ItemsSource="{Binding Variables}" SelectedIndex="-1" HorizontalContentAlignment="Stretch"
+                   AutomationProperties.Name="Variables list">
             <ListBox.ItemTemplate>
               <DataTemplate x:DataType="m:VariableItem">
-            <Grid ColumnDefinitions="Auto,*,Auto" Margin="4,2">
+                <Button Command="{Binding DataContext.InsertVariableCommand, RelativeSource={RelativeSource AncestorType=UserControl}}"
+                        CommandParameter="{Binding VariableName}"
+                        Background="Transparent" BorderThickness="0" Padding="8" MinHeight="44"
+                        AutomationProperties.Name="Insert variable">
+                  <Grid ColumnDefinitions="Auto,*,Auto">
                 <TextBlock Grid.Column="0" FontFamily="{StaticResource MDI}"
-                         FontSize="22" Text="{Binding Icon}" VerticalAlignment="Center" Margin="0,0,8,0" />
+                           FontSize="{DynamicResource IconSizeM}" Text="{Binding Icon}" VerticalAlignment="Center" Margin="0,0,8,0" />
                     <TextBlock Grid.Column="1" Text="{Binding VariableName}" FontWeight="Bold" VerticalAlignment="Center" />
-              <StackPanel Grid.Column="2" Spacing="2">
+                    <StackPanel Grid.Column="2" Spacing="6" VerticalAlignment="Center">
                       <TextBlock Text="{Binding Value}" />
                       <TextBlock IsVisible="{Binding IsExpression}" Text="{Binding ExpressionComputation}" FontStyle="Italic" />
                     </StackPanel>
                   </Grid>
+                </Button>
               </DataTemplate>
             </ListBox.ItemTemplate>
           </ListBox>
+          <TextBlock Text="No variables yet. Define with: x = 5"
+                     IsVisible="False"
+                     IsHitTestVisible="False"
+                     Opacity="0.6"
+                     HorizontalAlignment="Center" VerticalAlignment="Center">
+            <TextBlock.Styles>
+              <Style Selector="TextBlock">
+                <Style.Triggers>
+                  <DataTrigger Binding="{Binding Variables.Count}" Value="0">
+                    <Setter Property="IsVisible" Value="True" />
+                  </DataTrigger>
+                </Style.Triggers>
+              </Style>
+            </TextBlock.Styles>
+          </TextBlock>
+        </Grid>
 
         <!-- Function definitions -->
-      <ListBox Grid.Row="1" BorderThickness="0"
-               ItemsSource="{x:Static m:FunctionDefinitionItem.DefinedFunctions}">
+        <ListBox Grid.Row="1" BorderThickness="0" HorizontalContentAlignment="Stretch"
+                 ItemsSource="{x:Static m:FunctionDefinitionItem.DefinedFunctions}"
+                 AutomationProperties.Name="Functions list">
           <ListBox.ItemTemplate>
             <DataTemplate x:DataType="m:FunctionDefinitionItem">
-            <StackPanel Spacing="2" Margin="4,6">
-              <StackPanel Orientation="Horizontal" Spacing="6">
+              <Button Command="{Binding DataContext.InsertFunctionCommand, RelativeSource={RelativeSource AncestorType=UserControl}}"
+                      CommandParameter="{Binding FunctionName}"
+                      Background="Transparent" BorderThickness="0" Padding="8" MinHeight="44"
+                      AutomationProperties.Name="Insert function">
+                <StackPanel Spacing="8">
+                  <StackPanel Orientation="Horizontal" Spacing="8" VerticalAlignment="Center">
                     <TextBlock FontFamily="{StaticResource MDI}" Text="{Binding Icon}" />
                     <TextBlock Text="{Binding FunctionName}" FontWeight="Bold" />
                   </StackPanel>
@@ -59,43 +115,79 @@
                     </ItemsControl.ItemTemplate>
                   </ItemsControl>
                 </StackPanel>
+              </Button>
             </DataTemplate>
           </ListBox.ItemTemplate>
         </ListBox>
       </Grid>
+    </SplitView.Pane>
 
-    <!-- GridSplitter between columns -->
-    <GridSplitter Grid.Column="0" HorizontalAlignment="Right" Width="5" Background="Transparent" />
-
-    <!-- Right column: History + Input -->
-    <Grid Grid.Column="1" RowDefinitions="*,Auto">
+    <!-- Right content: History + Input -->
+    <SplitView.Content>
+      <Grid RowDefinitions="*,Auto">
         <!-- History -->
-      <ListBox Grid.Row="0" ItemsSource="{Binding History}" SelectedIndex="{Binding SelectedHistoryIndex}">
+        <Grid Grid.Row="0">
+          <ListBox ItemsSource="{Binding History}" SelectedIndex="{Binding SelectedHistoryIndex}"
+                   AutomationProperties.Name="History list">
             <ListBox.ItemTemplate>
               <DataTemplate x:DataType="m:HistoryItem">
                 <Grid ColumnDefinitions="Auto,*" Margin="4,2">
                 <TextBlock FontFamily="{StaticResource MDI}" Text="{x:Static m:IconFont.ArrowRightDropCircle}"
-                         FontSize="22" VerticalAlignment="Center" Margin="0,0,8,0" />
+                           FontSize="{DynamicResource IconSizeM}" VerticalAlignment="Center" Margin="0,0,8,0" />
                   <StackPanel Grid.Column="1">
-                <TextBlock Text="{Binding Input}" />
-                <TextBlock Text="{Binding Output}" FontWeight="Bold" />
+                    <TextBlock Text="{Binding Input}" MaxLines="3" />
+                    <TextBlock Text="{Binding Output}" FontWeight="Bold" MaxLines="2" />
                   </StackPanel>
                 </Grid>
               </DataTemplate>
             </ListBox.ItemTemplate>
           </ListBox>
+          <TextBlock Text="No history yet. Enter an expression and Evaluate."
+                     IsVisible="False"
+                     IsHitTestVisible="False"
+                     Opacity="0.6"
+                     HorizontalAlignment="Center" VerticalAlignment="Center">
+            <TextBlock.Styles>
+              <Style Selector="TextBlock">
+                <Style.Triggers>
+                  <DataTrigger Binding="{Binding History.Count}" Value="0">
+                    <Setter Property="IsVisible" Value="True" />
+                  </DataTrigger>
+                </Style.Triggers>
+              </Style>
+            </TextBlock.Styles>
+          </TextBlock>
+        </Grid>
 
         <!-- Input Row -->
-      <Grid Grid.Row="1" ColumnDefinitions="Auto,*" Margin="4">
-        <Button Command="{Binding ToggleFunctionsCommand}" Margin="0,0,6,0">
+        <Grid Grid.Row="1" ColumnDefinitions="Auto,Auto,*,Auto" Margin="4" ColumnSpacing="6">
+          <!-- Pane toggle: visible on narrow only -->
+          <ToggleButton Margin="0,0,6,0"
+                        IsVisible="{Binding $parent[Window].Bounds.Width,
+                                            Converter={StaticResource WidthToBooleanConverter},
+                                            ConverterParameter=640}"
+                        IsChecked="{Binding #RootSplit.IsPaneOpen}"
+                        AutomationProperties.Name="Open side panel">
+            <TextBlock Text="≡" FontSize="18"/>
+          </ToggleButton>
+
+          <!-- Toggle functions panel inside the pane -->
+          <Button Grid.Column="1" Command="{Binding ToggleFunctionsCommand}" Margin="0,0,6,0" MinHeight="40" MinWidth="40"
+                  AutomationProperties.Name="Toggle functions panel">
             <TextBlock FontFamily="{StaticResource MDI}" Text="{x:Static m:IconFont.Function}" />
           </Button>
-        <TextBox Grid.Column="1" Text="{Binding InputText, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}">
-          <InputElement.KeyBindings>
-            <KeyBinding Gesture="Enter" Command="{Binding SubmitCommand}" />
-          </InputElement.KeyBindings>
-        </TextBox>
-      </Grid>
+
+          <TextBox Grid.Column="2" Text="{Binding InputText, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" MinHeight="44"
+                   AutomationProperties.Name="Expression input"
+                   Watermark="Type an expression (e.g., 2 + 2)"/>
+          
+          <!-- Explicit evaluate button for touch -->
+          <Button Grid.Column="3" Command="{Binding SubmitCommand}" MinHeight="44" Padding="16,8"
+                  AutomationProperties.Name="Evaluate">
+            <TextBlock Text="Evaluate"/>
+          </Button>
         </Grid>
       </Grid>
+    </SplitView.Content>
+  </SplitView>
 </UserControl>