Design a Website Mockup

Hello, I create programming videos, and for many of the videos I need examples to create. The focus of my videos is not on the designs of the examples but instead of making them "dynamic." Attached I have a barebones version of an example application I want to make. As you can see, it's four different pages. What I need is a design that makes the app look good while retaining the same basic elements. The design shouldn't be complicated. It should just be easy to look at.