The biggest challenge was the length of the project. It was hard keeping track of all the various CSS variables and color changes. If I didn't have a step by step guide it would've been even more tedious to finish.
CSS Variables are useful when using repetitive styles. Even still it's helpful to have only a handful to remember. Also, gradients can manipulated to make pretty much anything. Even a moon.
Based on FreeCodeCamp's Responsive Web Design course.