Fix ordered list style

Sphynx outputs class information that corresponds to its generated
basic.css, which we do not include.  This results in all lists,
even nested lists, using arabic numerals.
Import the class properties into kerb.css for now.

doc/rst_source/_static/kerb.css

@@ -126,3 +126,25 @@ td.linenos pre {
     background-color: transparent;
     color: #aaa;
 }
+
+/* ordered lists */
+
+ol.arabic {
+    list-style: decimal;
+}
+
+ol.loweralpha {
+    list-style: lower-alpha;
+}
+
+ol.upperalpha {
+    list-style: upper-alpha;
+}
+
+ol.lowerroman {
+    list-style-type: lower-roman;
+}
+
+ol.upperroman {
+    list-style-type: upper-roman;
+}