Add test scene for demonstrating OsuDropdown appearance

osu.Game.Tests/Visual/UserInterface/TestSceneOsuDropdown.cs

@@ -0,0 +1,20 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using osu.Framework.Graphics;
+using osu.Game.Beatmaps;
+using osu.Game.Graphics.UserInterface;
+
+namespace osu.Game.Tests.Visual.UserInterface
+{
+    public class TestSceneOsuDropdown : ThemeComparisonTestScene
+    {
+        protected override Drawable CreateContent() =>
+            new OsuEnumDropdown<BeatmapSetOnlineStatus>
+            {
+                Anchor = Anchor.Centre,
+                Origin = Anchor.Centre,
+                Width = 150
+            };
+    }
+}