[css-counter-styles] Change decimal-leading-zero to use 'pad' rather than a fixed style.

Author: tabatkins

css-counter-styles/Overview.bs

@@ -1101,8 +1101,8 @@ Numeric: ''decimal'', ''decimal-leading-zero'', ''cjk-decimal'', ''lower-roman''
 	}
 
 	@counter-style decimal-leading-zero {
-		system: fixed -9;
-		symbols: '-09' '-08' '-07' '-06' '-05' '-04' '-03' '-02' '-01' '00' '01' '02' '03' '04' '05' '06' '07' '08' '09';
+		system: override decimal;
+		pad: 2 '0';
 	}
 
 	@counter-style cjk-decimal {

css-counter-styles/Overview.html

@@ -1135,8 +1135,8 @@ <h3 class="heading settled heading" data-level=6.1 id=simple-numeric><span class
 }
 
 @counter-style decimal-leading-zero {
-  system: fixed -9;
-  symbols: '-09' '-08' '-07' '-06' '-05' '-04' '-03' '-02' '-01' '00' '01' '02' '03' '04' '05' '06' '07' '08' '09';
+  system: override decimal;
+  pad: 2 '0';
 }
 
 @counter-style cjk-decimal {