As of Q3 2011, RadNotification allows the developer to set its size not only in pixels, but also in percent. This percentage is calculated from the browser's viewport.
This demo simulates a login page which welcomes the user and imitates several basic options for site navigation—the welcome bar at the top allows you to check for messages and also open a management panel.
Enter any user name and password and click login to begin.
All three RadNotifications have some dimensions set in percent and will, therefore, resize according to the browser size.