Simon Says almost done, need advice on design in general

So I’m almost done with my simon says project. There are a few bugs I’m trying to work out still such as I only want the colors to be highlighted if you click them when the machine is on and things kind of go haywire if you press a lot of buttons quickly. What I want advice on though is how to just make the design look better. I find that I do okay on the projects but when it comes to styling them they all kind of just look…bad. Any tips on how to make my designs look better? Or is this just going to be something that comes with time?

Here is the codepen
https://codepen.io/amthomps/pen/yzbXzE?editors=1111