[CSS21] typo.

Author: bert-github

css2/colors.src

@@ -84,7 +84,7 @@ for the root element.
 <!-- ToDo: ask the WG to validate the following text for erratum
 http://www.w3.org/Style/css2-updates/REC-CSS2-20110607-errata.html#s.14.2 -->
 
-<p>However, if the element whose backgound would be used for the
+<p>However, if the element whose background would be used for the
 background of the canvas has 'display: none', or is a descendant of an
 element with 'display: none', then the canvas background is
 undefined.