Use custom gtk theme when compiling and running on widows

EstusShots.Gtk/Program.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Runtime.InteropServices;
 using Gtk;
 
 namespace EstusShots.Gtk
@@ -10,6 +11,17 @@ namespace EstusShots.Gtk
         {
             Application.Init();
 
+            // Load a custom theme only when running on windows
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+            {
+                var provider = new CssProvider();
+                provider.LoadFromPath("Theme/gtk-3.20/gtk.css");
+                StyleContext.AddProviderForScreen(Gdk.Screen.Default, provider, 800);
+                
+                // TODO ????
+                //IconTheme.Default.PrependSearchPath("Theme/icons/48x48");
+            }
+            
             var app = new Application("EstusShots.Gtk", GLib.ApplicationFlags.None);
             app.Register(GLib.Cancellable.Current);