Update runtime files.

runtime/doc/gui_x11.txt

@@ -376,8 +376,8 @@ 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):
+following snippet of CSS code to $XDG_HOME_DIR/gtk-3.0/gtk.css (see the next
+section):
 
 For GTK+ 3 < 3.20: >
 
@@ -408,6 +408,10 @@ stable support for GTK+ CSS:
 GTK+ uses CSS for styling and layout of widgets.  In this subsection, we'll
 have a quick look at GTK+ CSS through simple, illustrative examples.
 
+You can usually edit the config with: >
+	vim $HOME/.config/gtk-3.0/gtk.css
+
+
 Example 1.  Empty Space Adjustment ~
 
 By default, the toolbar and the tabline of the GTK+ 3 GUI are somewhat larger
@@ -492,6 +496,16 @@ unexpectedly less attractive or even deteriorates their usability.  Keep this
 in mind always when you try improving a theme.
 
 
+Example 3.  border color
+
+To eliminate borders when maximized: >
+
+    @define-color bg_color #1B2B34;
+    #vim-main-window {
+	background-color: @bg_color;
+    }
+
+
 Using Vim as a GTK+ plugin ~
 							*gui-gtk-socketid*
 When the GTK+ version of Vim starts up normally, it creates its own top level