Portal does not apply to any class. While defining a portal, we enter only the name and the ruleset it is associated to. A portal mainly contains harness(for its content) and skin(for styling). We define class name for the harness and not for the skin rule as it does not have an applies to class. It is recommended that we use Data-Portal as the class name for the harness as all the sections in Case Worker and Case Manager portals are defined in Data-Portal class, so we can reuse them if we define the harness in the same class.
Adding points to the shilpiroy, after creating your own portals make sure the styling should not effect the entire application.You have to create your own skin in your application ruleset if any changes want in the slin rule.So that the changes will not effect the default skin.At the portal creation also pega will ask the skin type.