Update text-contrast-afw4f7.md

Author: giacomo-petri

_rules/text-contrast-afw4f7.md

@@ -301,7 +301,7 @@ This text in a [semantic button][semantic role] has a contrast ratio of 3.85:1.
 The grey text has a contrast between 2.7:1 and 2.9:1 against the grey text shadow.
 
 ```html
-<p style="color: #666; text-shadow: #aaa 2px 2px 4px, #aaa -2px 2px 4px, #aaa 2px -2px 4px, #aaa -2px -2px 4px;">
+<p style="color: background: #fff; #666; text-shadow: #aaa 2px 2px 4px, #aaa -2px 2px 4px, #aaa 2px -2px 4px, #aaa -2px -2px 4px;">
     Some text in a human language
   </p>
 ```