If you want to customize your course's appearance, there are a few ways to do this.
The easiest way to change your course's appearance is to change your course's theme. This can be accomplished by clicking on the color fan in the upper right-hand corner and select a theme.
There are additional settings in the Teaching Style section located in Customization on the left-navigation bar. Here, you can choose a course structure, the entry point to your course, course theme (like above), the left-hand navigation menu style, and even add a banner to your course. Feel free to play with these options as they will change the look-and-feel of your course, but will not affect the content in your course.