lightweight variant (#1)

Reviewed-on: #1
Co-authored-by: Aleksandr Neychev <alexnejchev73@gmail.com>

CursorLang.Settings/Interop/WindowThemeNative.cs

@@ -0,0 +1,30 @@
+using System.Runtime.InteropServices;
+
+namespace CursorLang.Settings.Interop;
+
+/// <summary>
+/// Window frame styling by the system: the title bar is drawn by Windows,
+/// and in the dark theme it has to be switched separately from the window content.
+/// </summary>
+internal static class WindowThemeNative
+{
+    [DllImport("dwmapi.dll")]
+    private static extern int DwmSetWindowAttribute(IntPtr hWnd, int attribute, ref int value, int size);
+
+    private const int DWMWA_USE_IMMERSIVE_DARK_MODE = 20;
+
+    /// <summary>
+    /// Recolours the window title bar. On Windows 10 builds before 2004 the attribute
+    /// is not supported — the title bar simply stays light.
+    /// </summary>
+    internal static void SetDarkTitleBar(IntPtr hWnd, bool isDark)
+    {
+        if (hWnd == IntPtr.Zero)
+        {
+            return;
+        }
+
+        int value = isDark ? 1 : 0;
+        DwmSetWindowAttribute(hWnd, DWMWA_USE_IMMERSIVE_DARK_MODE, ref value, sizeof(int));
+    }
+}