[css-lists] Use calc() rather than increment hacks.

Author: tabatkins

css-lists/Overview.bs

@@ -1305,8 +1305,7 @@ Sample style sheet for HTML</h2>
 
 		/* The start attribute on ol elements */
 		ol[start] {
-			counter-reset: list-item attr(start integer, 1);
-			counter-increment: list-item -1;
+			counter-reset: list-item calc(attr(start integer, 1) - 1);
 		}
 
 		/* The value attribute on li elements */
@@ -1317,9 +1316,8 @@ Sample style sheet for HTML</h2>
 
 		/* Handling reversed lists */
 		ol[reversed] {
-			counter-reset: list-item attr(start integer, **magic**);
+			counter-reset: list-item calc(attr(start integer, **magic**) + 1);
 			/* Where **magic** is the number of child &lt;li> elements. */
-			counter-increment: list-item -1;
 		}
 		ol[reversed] > li {
 			counter-increment: list-item -1;

css-lists/Overview.html

@@ -1321,8 +1321,7 @@ <h2 class="heading settled heading" data-level=10 id=ua-stylesheet><span class=s
 
   /* The start attribute on ol elements */
   ol[start] {
-    counter-reset: list-item attr(start integer, 1);
-    counter-increment: list-item -1;
+    counter-reset: list-item calc(attr(start integer, 1) - 1);
   }
 
   /* The value attribute on li elements */
@@ -1333,9 +1332,8 @@ <h2 class="heading settled heading" data-level=10 id=ua-stylesheet><span class=s
 
   /* Handling reversed lists */
   ol[reversed] {
-    counter-reset: list-item attr(start integer, **magic**);
+    counter-reset: list-item calc(attr(start integer, **magic**) + 1);
     /* Where **magic** is the number of child &lt;li&gt; elements. */
-    counter-increment: list-item -1;
   }
   ol[reversed] &gt; li {
     counter-increment: list-item -1;