add css class for horizontal lists

sass/_default.scss

@@ -177,20 +177,10 @@ a{
 }
 
 $topnav_color: $ACCENT_COLOR !default;
-$topnav_list_margin_left: 0 !default;
 #topnav {
   @include navbar($topnav_color);
   justify-content: space-between;
   align-items: baseline;
-
-  & ul {
-    display: inline;
-    margin-left: $topnav_list_margin_left;
-  }
-
-  & ul li {
-    display: inline list-item;
-  }
 }
 
 $bottomnav_color: $DARK_1 !default;
@@ -1083,6 +1073,16 @@ ul, ol {
   padding: $list_padding;
 }
 
+$horizontal_list_margin_left: 0 !default;
+ul.horizontal, ol.horizontal {
+  display: inline;
+  margin-left: $horizontal_list_margin_left;
+  & li {
+    display: inline list-item;
+  }
+}
+
+
 .new-concept-notification.hidden {
   display: none;
 }