When you "style" an app, you are controlling the overall look of the app. You begin from the "Style" tab or from the [Edit Page Style] button.
You will be able to choose the page’s Header Image, Profile Image, Title, Description, and Background Color. All are optional, so you can have a profile without a Header Image, a Title without images, etc.
You will also be able to select the background color and text color for Actions, which will give the Actions a consistent look, but the indiviudal Actions will also have their own styling aptions. See the Actions formatting options here.
The first image below shows the controls on the Style Editing page. The second image shows the display of a sample app.
[Save] when you get the look you want. Edit at any time in the future.