Go and take a look here! -> Link
Simon Says is a game where the computer (Simon) will tell you a sequence of colors you should follow. If you follow the sequence correctly, you will win the round. Each one of the rounds will turn into a more difficult sequence to follow. Once you win a n number of rounds, you will win the game.
The three HTML, CSS and JavaScript are added to the same index.html file. Nonetheless, in the folder components, you'll see each one of the files that were created for the game in its extension.
P.S. This game was created using HTML5, CSS3 and JavaScript Vanilla (no frameworks nor libraries extra).