first commit

Nitrox.Launcher/Views/Abstract/ModalBase.cs

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+using Avalonia.Controls;
+
+namespace Nitrox.Launcher.Views.Abstract;
+
+public abstract class ModalBase : Window
+{
+    protected override void OnInitialized() => this.ApplyOsWindowStyling();
+}

Nitrox.Launcher/Views/Abstract/RoutableViewBase.cs

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+using Avalonia.Controls;
+using Nitrox.Launcher.ViewModels.Abstract;
+
+namespace Nitrox.Launcher.Views.Abstract;
+
+public abstract class RoutableViewBase<TViewModel> : UserControl
+    where TViewModel : RoutableViewModelBase;

Nitrox.Launcher/Views/Abstract/WindowEx.cs

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+using System;
+using Avalonia.Controls;
+using Nitrox.Launcher.Models.Design;
+using Nitrox.Launcher.ViewModels.Abstract;
+
+namespace Nitrox.Launcher.Views.Abstract;
+
+public abstract class WindowEx<T> : Window where T : ViewModelBase
+{
+    protected override void OnInitialized()
+    {
+        this.ApplyOsWindowStyling();
+
+        // On Linux systems, Avalonia has trouble allowing windows to resize without "decorations". So we enable it in full, but hide the custom titlebar as it'll look bad.
+        if (OperatingSystem.IsLinux())
+        {
+            SystemDecorations = SystemDecorations.Full;
+            NitroxAttached.SetUseCustomTitleBar(this, false);
+        }
+    }
+}