Fix bottom margin for notes (github#32285)

Author: gracepark

stylesheets/extended-markdown.scss

@@ -29,8 +29,8 @@
   &.warning,
   &.tip,
   &.danger {
-    p {
-      margin: 0;
+    p:last-child {
+      margin-bottom: 0;
     }
   }
 }