Updated the ContentView view in the app target to support navigation split view and to show floating new task button on both sidebar and details views when required.

App/Sources/Views/ContentView.swift

@@ -4,13 +4,14 @@ import SwiftUI
 /// The main content view of the app.
 ///
 /// This view serves as the primary interface for managing todo tasks.
-///
-/// The view uses a dedicated view model (`ViewModel`) to manage state and business logic, following the MVVM pattern.
-/// User interactions are handled through the view model, maintaining separation of concerns.
 struct ContentView: View {
 
     // MARK: Properties
 
+    /// The horizontal size class of the environment.
+    @Environment(\.horizontalSizeClass)
+    private var horizontalSizeClass
+
     /// The view model managing the state and logic for this view.
     @State
     private var viewModel = ViewModel()
@@ -19,30 +20,38 @@ struct ContentView: View {
 
     /// The content and behavior of the view.
     ///
-    /// Displays a navigation view containing:
+    /// Displays a navigation split view with:
+    /// - Sidebar: List of todo task groups
+    /// - Detail: List of todo task related to a selected todo task group
     /// - A floating action button for adding new tasks
     ///
-    /// The view presents a sheet when `viewModel.newTaskShown` is true,
-    /// allowing users to create new todo tasks.
+    /// The view presents a sheet to allow users to create new todo tasks.
     var body: some View {
-        NavigationView {
-            ZStack(alignment: .bottomTrailing) {
-                TaskGroupListView()
-
-                Button(action: viewModel.showNewTask) {
-                    Image(systemName: "plus")
-                        .frame(width: 48, height: 48)
-                        .foregroundStyle(.white)
+        NavigationSplitView {
+            TaskGroupListView($viewModel.group)
+                .newTaskButton(show: viewModel.showNewTaskButtonInSidebar(when: horizontalSizeClass)) {
+                    viewModel.showNewTask()
                 }
-                .glassEffect(.regular.tint(.blue.opacity(0.8)).interactive())
-                .padding(.trailing, 20)
+        } detail: {
+            if let group = viewModel.group {
+                TaskListView(group: group)
+                    .newTaskButton(show: viewModel.showNewTaskButtonInDetails) {
+                        viewModel.showNewTask()
+                    }
+                    .sheet(isPresented: $viewModel.newTaskShown) {
+                        NewTaskView()
+                    }
+            }
+            else {
+                ContentUnavailableView(
+                    "Select a Group",
+                    systemImage: "sidebar.left",
+                    description: Text("Choose a task group from the sidebar")
+                )
             }
-            .navigationTitle("Todos")
-        }
-        .sheet(isPresented: $viewModel.newTaskShown) {
-            NewTaskView()
         }
     }
+
 }
 
 // MARK: - Previews