[css-counter-styles] Slightly reword the prefix descriptor to fix Roland's issue.

Author: tabatkins

css-counter-styles/Overview.html

@@ -1030,7 +1030,7 @@ <h3 id=counter-style-prefix><span class=secno>3.3. </span> Symbols before
    algorithm for constructing the default contents of the ‘<code
    class=css>::marker</code>’ pseudo-element; the prefix is not added
    automatically when the counter() or counters() functions are used.
-   Prefixes are added to the representation after negative signs.
+   Prefixes come before any negative sign.
 
   <h3 id=counter-style-suffix><span class=secno>3.4. </span> Symbols after
    the marker: the ‘<a href="#descdef-suffix"><code

css-counter-styles/Overview.src.html

@@ -740,7 +740,7 @@ <h3 id='counter-style-prefix'>
 	marker representation.  Prefixes are only added by the algorithm for constructing
 	the default contents of the ''::marker'' pseudo-element; the prefix is not 
 	added automatically when the counter() or counters() functions are used.  
-	Prefixes are added to the representation after negative signs.
+	Prefixes come before any negative sign.
 
 
 <h3 id='counter-style-suffix'>