You can also use our style helper to remove the stylesheet and use your own.
In a way you copy the file to the skin folder and edit it.
That means you don't have to worry about upgrades overwriting your edits

Steps:

1. Install the latest version of our stylehelper: https://stylehelper.codeplex.com/
2. Add this to your skin:

<%@ Register TagPrefix="fortyfingers" TagName="STYLEHELPER" Src="~/DesktopModules/40Fingers/SkinObjects/StyleHelper/StyleHelper.ascx" %>
<fortyfingers:STYLEHELPER ID="SH2" IfUserMode="Edit" RemoveCssFile="dnn.dragDrop.css" AddCssFile="[S]dnn.dragDrop.css" runat="server" />

3. Copy the dnn.dragDrop.css file to your skin folder
4. Remove the first line from you local copy of the stylesheet.

HTH Timo