As a Page Manager: 
  1. Navigate to onMessage.
  2. Select Website > Your Site.
  3. Click Master Layouts.
  4. Select your Master Layout.
  5. Click the paintbrush/Styles icon in the upper left corner. 
  6. At the bottom of the window, click Edit Styles and select Regions.
  7. Click in your region and use the APpliAppliede drop down in the upper left to select your style.
  8. Click Apply Changes.