You can further customize the look / feel of your story map through the Design menu.
Open the story map that you would like to edit. Click Design, located in the top menu bar.
The design menu will open as a sidebar panel. Use the settings in the design panel to change your story map's cover, theme, etc. We recommend enabling the Navigation bar under the optional story sections. This setting will create a menu bar at the top of your story map that lets viewers quickly navigate to the different headings for your story.
StoryMaps provides 6 default themes if you want to change the colors / fonts used in your story map.
If you don't like any of the default themes, you can click Browse My Themes to create your own custom theme in the theme builder.