patch 7.4.1402
Problem:    GTK 3 is not supported.
Solution:   Add GTK 3 support. (Kazunobu Kuriyama)
diff --git a/runtime/doc/gui_x11.txt b/runtime/doc/gui_x11.txt
index f085e2f..605b998 100644
--- a/runtime/doc/gui_x11.txt
+++ b/runtime/doc/gui_x11.txt
@@ -369,6 +369,16 @@
 you might have to use the file ~/.gtkrc-2.0 instead, depending on your
 distribution.
 
+For GTK+ 3, an effect similar to the above can be obtained by adding the
+following snippet of CSS code to $XDG_HOME_DIR/gtk-3.0/gtk.css (usually,
+$HOME/.config/gtk-3.0/gtk.css):
+ >
+	.tooltip {
+		background-color: #ffffcc;
+		color: #000000;
+	}
+<
+
 Using Vim as a GTK+ plugin				*gui-gtk-socketid*
 
 When the GTK+ version of Vim starts up normally, it creates its own top level