Piano player issue

Hello all,

I am having issues with this project. Here is my code:

// The keys and notes variables store the piano keys
const keys = ['c-key', 'd-key', 'e-key', 'f-key', 'g-key', 'a-key', 'b-key', 'high-c-key', 'c-sharp-key', 'd-sharp-key', 'f-sharp-key', 'g-sharp-key', 'a-sharp-key'];
const notes = [];

// Write named functions that change the color of the keys below
const keyPlay = function(event) {
  event.target.style.backgroundColor = '#6df0c2';

const keyReturn = function(event) {
  event.target.style.backgroundColor = '';

// Write a named function with event handler properties
let eventAssignment = function(note) {
  note.onmousedown = function() {
  note.onmouseup = function() {

// Write a loop that runs the array elements through the function

// These variables store the buttons that progress the user through the lyrics
let nextOne = document.getElementById('first-next-line');
let nextTwo = document.getElementById('second-next-line');
let nextThree = document.getElementById('third-next-line');
let startOver = document.getElementById('fourth-next-line');

// This variable stores the '-END' lyric element
let lastLyric = document.getElementById('column-optional');

// These statements are "hiding" all the progress buttons, but the first one
nextTwo.hidden = true;
nextThree.hidden = true;
startOver.hidden= true;

// Write anonymous event handler property and function for the first progress button

// Write anonymous event handler property and function for the second progress button

// Write anonymous event handler property and function for the third progress button

// This is the event handler property and function for the startOver button
startOver.onclick = function() {
  nextOne.hidden = false;
  startOver.hidden = true;
   document.getElementById('word-one').innerHTML = 'HAP-';
  document.getElementById('letter-note-one').innerHTML = 'G';
  document.getElementById('word-two').innerHTML = 'PY';
  document.getElementById('letter-note-two').innerHTML = 'G';
  document.getElementById('word-three').innerHTML = 'BIRTH-';
  document.getElementById('letter-note-three').innerHTML = 'A';
  document.getElementById('word-four').innerHTML = 'DAY';
  document.getElementById('letter-note-four').innerHTML = 'G';
  document.getElementById('word-five').innerHTML = 'TO';
  document.getElementById('letter-note-five').innerHTML = 'C';
  document.getElementById('word-six').innerHTML = 'YOU!';
  document.getElementById('letter-note-six').innerHTML = 'B';

The code is not changing the background color on mouse down or up. Nothing is happening I have tried it on scrim and it works which is super strange. This is a letter for letter copy from the video.

Any help would be greatly appreciated.

When is that function called?