How to remove custom styles from modal pop up windows in SharePoint 2010

When you create a custom masterpage and add new elements, it adds the new elements to the pop up window i.e. add new page pop up window

When the pop up window looks like the image below after you have created a custom master pages and want to remove all the custom styles as this can conflict with all your dialog boxes.

The Fix:

How you remove this custom banner with simple class called: .s4-notdlg

Example:

<div class="s4-notdlg customClass">Here is my custom header</div>

The Results: