Rename all DropDown -> Dropdown.

osu.Game/Graphics/UserInterface/OsuDropdown.cs

@@ -0,0 +1,40 @@
+// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using System.Linq;
+using OpenTK.Graphics;
+using osu.Framework.Allocation;
+using osu.Framework.Graphics.UserInterface;
+
+namespace osu.Game.Graphics.UserInterface
+{
+    public class OsuDropdown<T> : Dropdown<T>
+    {
+        protected override DropdownHeader CreateHeader() => new OsuDropdownHeader { AccentColour = AccentColour };
+
+        protected override Menu CreateMenu() => new OsuMenu();
+
+        private Color4? accentColour;
+        public virtual Color4 AccentColour
+        {
+            get { return accentColour.GetValueOrDefault(); }
+            set
+            {
+                accentColour = value;
+                if (Header != null)
+                    ((OsuDropdownHeader)Header).AccentColour = value;
+                foreach (var item in MenuItems.OfType<OsuDropdownMenuItem<T>>())
+                    item.AccentColour = value;
+            }
+        }
+
+        [BackgroundDependencyLoader]
+        private void load(OsuColour colours)
+        {
+            if (accentColour == null)
+                AccentColour = colours.PinkDarker;
+        }
+
+        protected override DropdownMenuItem<T> CreateMenuItem(string text, T value) => new OsuDropdownMenuItem<T>(text, value) { AccentColour = AccentColour };
+    }
+}