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HTML 

              
                <div>♬</div>

<!-- animation controls -->
<form>
  <p>
  <input type="checkbox" id="pauser" checked>
  <label for="pauser">Animate</label>
  </p>
</form>
!

CSS 

              
                div, div::before, div::after {
  position: relative;
  box-sizing: border-box;
}

div {
  --color1: hsl(196, 50%, 50%);
  --color1alt: hsl(196, 50%, 33%);
  --color1alta: hsl(196, 50%, 73%);
  --color2: hsl(356, 70%, 50%);
  --color2alt: hsl(356, 70%, 40%);
  --color2alta: hsl(356, 70%, 80%);
  --color3: hsl(33, 80%, 60%);
  --color3alt: hsl(43, 80%, 50%);
  --white: #eaeaef;
  --white-between: hsla(0,0%,0%,.2);
  --black: var(--color1alt);
  
  --height: 40vmin;
  --bellow-y: 1vmin;
  --bellow-y-less: 39vmin;
  --bellow-width: 50vmin;
  
  --button-dim: 1.4vmin;
  --button: radial-gradient(circle, var(--color1) var(--button-dim), transparent var(--button-dim));
  --button1: radial-gradient(circle, var(--button1-color, var(--color1)) var(--button1-dim, var(--button-dim)), transparent var(--button1-dim, var(--button-dim)));
  --button4: radial-gradient(circle, var(--button4-color, var(--color1)) var(--button4-dim, var(--button-dim)), transparent var(--button4-dim, var(--button-dim)));
  --button7: radial-gradient(circle, var(--button7-color, var(--color1)) var(--button7-dim, var(--button-dim)), transparent var(--button7-dim, var(--button-dim)));
  --button8: radial-gradient(circle, var(--button8-color, var(--color1)) var(--button8-dim, var(--button-dim)), transparent var(--button8-dim, var(--button-dim)));
  --button-x: -3vmin;
  --button-y: -16vmin;
  --button2-x: 2vmin; --button2-y: -12vmin;
  --button3-y: -8vmin;
  --button4-x: 2vmin; --button4-y: -4vmin;
  --button5-y: 0vmin;
  --button6-x: 2vmin; --button6-y: 4vmin;
  --button7-y: 8vmin;
  --button8-x: 2vmin; --button8-y: 12vmin;
  --button9-y: 16vmin;
  
  --button-key-x: 5.5vmin;
  --button-key1-y: -6vmin;
  --button-key2-y: 0vmin;
  --button-key3-y: 6vmin;
   
  --shine: linear-gradient(to bottom, transparent 11.5%, var(--color2) 11.5%, var(--color2) 29.5%, transparent 29.5%, transparent 70.5%, var(--color2) 70.5%, var(--color2) 88.5%, transparent 88.5%);
  --shine-horizontal: linear-gradient(to right, transparent 9.5%, var(--color2) 41.5%, var(--color2) 58.5%, transparent 86.5%);
  
  --the-black-keys: 
    linear-gradient(
      to bottom,
      transparent 3.5%,
      var(--black1, var(--black)) 3.5%,
      var(--black1, var(--black)) 6.5%,
      transparent 6.5%,
      transparent 8.5%,
      var(--black2, var(--black)) 8.5%,
      var(--black2, var(--black)) 11.5%,
      transparent 11.5%,
      transparent 13.5%,
      var(--black3, var(--black)) 13.5%,
      var(--black3, var(--black)) 16.5%,
      transparent 16.5%,
      
      transparent 23.5%,
      var(--black4, var(--black)) 23.5%,
      var(--black4, var(--black)) 26.5%,
      transparent 26.5%,
      transparent 28.5%,
      var(--black5, var(--black)) 28.5%,
      var(--black5, var(--black)) 31.5%,
      transparent 31.5%,
      
      transparent 38.5%,
      var(--black6, var(--black)) 38.5%,
      var(--black6, var(--black)) 41.5%,
      transparent 41.5%,
      transparent 43.5%,
      var(--black7, var(--black)) 43.5%,
      var(--black7, var(--black)) 46.5%,
      transparent 46.5%,
      transparent 48.5%,
      var(--black8, var(--black)) 48.5%,
      var(--black8, var(--black)) 51.5%,
      transparent 51.5%,
      
      transparent 58.5%,
      var(--black9, var(--black)) 58.5%,
      var(--black9, var(--black)) 61.5%,
      transparent 61.5%,
      transparent 63.5%,
      var(--black10, var(--black)) 63.5%,
      var(--black10, var(--black)) 66.5%,
      transparent 66.5%,
      
      
      transparent 73.5%,
      var(--black11, var(--black)) 73.5%,
      var(--black11, var(--black)) 76.5%,
      transparent 76.5%,
      transparent 78.5%,
      var(--black12, var(--black)) 78.5%,
      var(--black12, var(--black)) 81.5%,
      transparent 81.5%,
      transparent 83.5%,
      var(--black13, var(--black)) 83.5%,
      var(--black13, var(--black)) 86.5%,
      transparent 86.5%,
      
      transparent 93.5%,
      var(--black14, var(--black)) 93.5%,
      var(--black14, var(--black)) 96.5%,
      transparent 96.5%
    );
  
  /* If not animating, the keys can be done with a repeating linear gradient, breaking it out explicity (a few lines down) allows us more animation options 
  --keyboard: repeating-linear-gradient(to bottom, 
      var(--white-between) 0%,
      var(--white-between) 0.4%,
      var(--white) 0.4%,
      var(--white) 5%);
  */
  
  --keyboard: linear-gradient(to bottom, 
      var(--white-between) 0%,
      var(--white-between) 0.4%,
      var(--white1, var(--white)) 0.4%,
      var(--white1, var(--white)) 5%, 
      var(--white-between) 5%,
      var(--white-between) 5.4%,
      var(--white2, var(--white)) 5.4%,
      var(--white2, var(--white)) 10%, 
      var(--white-between) 10%,
      var(--white-between) 10.4%,
      var(--white3, var(--white)) 10.4%,
      var(--white3, var(--white)) 15%, 
      var(--white-between) 15%,
      var(--white-between) 15.4%,
      var(--white4, var(--white)) 15.4%,
      var(--white4, var(--white)) 20%, 
      var(--white-between) 20%,
      var(--white-between) 20.4%,
      var(--white5, var(--white)) 20.4%,
      var(--white5, var(--white)) 25%, 
      var(--white-between) 25%,
      var(--white-between) 25.4%,
      var(--white6, var(--white)) 25.4%,
      var(--white6, var(--white)) 30%, 
      var(--white-between) 30%,
      var(--white-between) 30.4%,
      var(--white7, var(--white)) 30.4%,
      var(--white7, var(--white)) 35%, 
      var(--white-between) 35%,
      var(--white-between) 35.4%,
      var(--white8, var(--white)) 35.4%,
      var(--white8, var(--white)) 40%, 
      var(--white-between) 40%,
      var(--white-between) 40.4%,
      var(--white9, var(--white)) 40.4%,
      var(--white9, var(--white)) 45%, 
      var(--white-between) 45%,
      var(--white-between) 45.4%,
      var(--white10, var(--white)) 45.4%,
      var(--white10, var(--white)) 50%, 
      var(--white-between) 50%,
      var(--white-between) 50.4%,
      var(--white11, var(--white)) 50.4%,
      var(--white11, var(--white)) 55%, 
      var(--white-between) 55%,
      var(--white-between) 55.4%,
      var(--white12, var(--white)) 55.4%,
      var(--white12, var(--white)) 60%, 
      var(--white-between) 60%,
      var(--white-between) 60.4%,
      var(--white13, var(--white)) 60.4%,
      var(--white13, var(--white)) 65%, 
      var(--white-between) 65%,
      var(--white-between) 65.4%,
      var(--white14, var(--white)) 65.4%,
      var(--white14, var(--white)) 70%, 
      var(--white-between) 70%,
      var(--white-between) 70.4%,
      var(--white15, var(--white)) 70.4%,
      var(--white15, var(--white)) 75%, 
      var(--white-between) 75%,
      var(--white-between) 75.4%,
      var(--white16, var(--white)) 75.4%,
      var(--white16, var(--white)) 80%, 
      var(--white-between) 80%,
      var(--white-between) 80.4%,
      var(--white17, var(--white)) 80.4%,
      var(--white17, var(--white)) 85%, 
      var(--white-between) 85%,
      var(--white-between) 85.4%,
      var(--white18, var(--white)) 85.4%,
      var(--white18, var(--white)) 90%, 
      var(--white-between) 90%,
      var(--white-between) 90.4%,
      var(--white19, var(--white)) 90.4%,
      var(--white19, var(--white)) 95%, 
      var(--white-between) 95%,
      var(--white-between) 95.4%,
      var(--white20, var(--white)) 95.4%,
      var(--white20, var(--white)) 100%);
  
  --keyboard-base: linear-gradient(to right, var(--color3alt), var(--color3alt));
  
  --black-keys-position: 45% center;
  --black-keys-size: 36% 84%;
  --keyboard-position: left center;
  --keyboard-size: 66% 84%;
  
  --squeeze-duration: 13000ms;
  --button-duration: 2300ms;
  --squeeze-state: running;
  
  --note-color1: rgba(255, 255, 255, .1);
  --note-color2: rgba(255, 255, 255, .2);
  --note-color3: rgba(255, 255, 255, .05);
  --note-x1: -10vmin;
  --note-x2: -16vmin;
  --note-x3: -8vmin;
  
  --notes-full-1: var(--note-x1) 5vmin 0vmin var(--note-color1),
    var(--note-x2) 25vmin 0vmin var(--note-color2),
    var(--note-x3) 37.5vmin 0vmin var(--note-color3);
  --notes-full-2: -8vmin 5vmin 0vmin rgba(255, 255, 255, .4),
      -10vmin 25vmin 0vmin rgba(255, 255, 255, .02),
      -14vmin 37.5vmin 0vmin rgba(255, 255, 255, .24);
  --notes-full-3: -12vmin 5vmin 0vmin rgba(255, 255, 255, .1),
      -8vmin 25vmin 0vmin rgba(255, 255, 255, .2),
      -16vmin 37.5vmin 0vmin rgba(255, 255, 255, .4);
  --notes-full-4: -16vmin 5vmin 0vmin rgba(255, 255, 255, .2),
      -13vmin 25vmin 0vmin rgba(255, 255, 255, .3),
      -9vmin 37.5vmin 0vmin rgba(255, 255, 255, .1);
}

/*keyboard side*/
div {
  width: calc(var(--bellow-width) * .36);
  height: calc(var(--height) + 5vmin);
  border-radius: 4vmin 1vmin 1vmin 4vmin;
  border: 0vmin solid var(--color2);
 
  background:
    var(--shine),
    var(--shine),
    var(--button-key1, var(--button)),
    var(--button-key2, var(--button)),
    var(--button-key3, var(--button)),
    var(--the-black-keys),
    var(--keyboard),
    var(--keyboard-base);
  background-repeat: no-repeat;
  
  background-position:
    80% 0,
    85% 0,
    var(--button-key-x) var(--button-key1-y),
    var(--button-key-x) var(--button-key2-y),
    var(--button-key-x) var(--button-key3-y),
    var(--black-keys-position),
    var(--keyboard-position),
    0 0;
  
  background-size:
    1px 100%,
    2px 100%,
    100%,
    100%,
    100%,
    var(--black-keys-size),
    var(--keyboard-size),
    100%;
  
  box-shadow: inset 1vmin 0px 0 1vmin rgba(235,235,239,.2);
  
  transform: translateX(calc(var(--bellow-width) * -.66));
  
  text-shadow: var(--notes-full-1);
  
  color: rgba(0,0,0,0);
  font-size: 4vmin;
}

/* bellows */
div::before{
  width: var(--bellow-width);
  height: var(--height);
  background:
    linear-gradient(to right, rgba(255, 255, 255, 0), rgba(255, 255, 255, .02)),
    repeating-linear-gradient(to right, var(--color1) 0vmin, var(--color1) 2.5vmin, var(--color1alt) 2.5vmin, var(--color1alt) 5vmin);
  top: 2.5vmin;
  left: 100%;
  bottom: 0;
}

@supports(clip-path: polygon(0% 0%, 0% 10%, 10% 0%)) {
  div::before {  
    clip-path: polygon(
      0% 0%, 
      2.5vmin var(--bellow-y), 
      5vmin 0, 
      7.5vmin var(--bellow-y), 
      10vmin 0, 
      12.5vmin var(--bellow-y), 
      15vmin 0, 
      17.5vmin var(--bellow-y), 
      20vmin 0, 
      22.5vmin var(--bellow-y), 
      25vmin 0, 
      27.5vmin var(--bellow-y), 
      30vmin 0, 
      32.5vmin var(--bellow-y), 
      35vmin 0, 
      37.5vmin var(--bellow-y), 
      40vmin 0, 
      42.5vmin var(--bellow-y), 
      45vmin 0, 
      47.5vmin var(--bellow-y), 
      50vmin 0,
      50vmin var(--height),
      47.5vmin var(--bellow-y-less),
      45vmin var(--height),
      42.5vmin var(--bellow-y-less),
      40vmin var(--height),
      37.5vmin var(--bellow-y-less),
      35vmin var(--height),
      32.5vmin var(--bellow-y-less),
      30vmin var(--height),
      27.5vmin var(--bellow-y-less),
      25vmin var(--height),
      22.5vmin var(--bellow-y-less),
      20vmin var(--height),
      17.5vmin var(--bellow-y-less),
      15vmin var(--height),
      12.5vmin var(--bellow-y-less),
      10vmin var(--height),
      7.5vmin var(--bellow-y-less),
      5vmin var(--height),
      2.5vmin var(--bellow-y-less),
      0vmin var(--height)
    );
  }
}

/* button side */
div::after {
  left: calc(100% + var(--bellow-width));
  top: 0;
  bottom: 0;
  width: calc(var(--bellow-width) * .30);
  border-radius: 1vmin 4vmin 4vmin 1vmin; 
  
  background:
    var(--shine-horizontal),
    var(--shine-horizontal),
    var(--button1, var(--button)),
    var(--button2, var(--button)),
    var(--button3, var(--button)),
    var(--button4, var(--button)),
    var(--button5, var(--button)),
    var(--button6, var(--button)),
    var(--button7, var(--button)),
    var(--button8, var(--button)),
    var(--button9, var(--button)),
    linear-gradient(var(--color3alt), var(--color3alt));
  background-repeat: no-repeat;
  
  background-position: 
    1.5vmin 8%,
    1.5vmin 92%,
    var(--button1-x, var(--button-x)) var(--button1-y, var(--button-y)),
    var(--button2-x, var(--button-x)) var(--button2-y, var(--button-y)),
    var(--button3-x, var(--button-x)) var(--button3-y, var(--button-y)),
    var(--button4-x, var(--button-x)) var(--button4-y, var(--button-y)),
    var(--button5-x, var(--button-x)) var(--button5-y, var(--button-y)),
    var(--button6-x, var(--button-x)) var(--button6-y, var(--button-y)),
    var(--button7-x, var(--button-x)) var(--button7-y, var(--button-y)),
    var(--button8-x, var(--button-x)) var(--button8-y, var(--button-y)),
    var(--button9-x, var(--button-x)) var(--button9-y, var(--button-y)),
    center center;
  
  --default-size: 100%;
  
  background-size:
    80% 2px,
    80% 2px,
    var(--default-size),
    var(--default-size),
    var(--default-size),
    var(--default-size),
    var(--default-size),
    var(--default-size),
    var(--default-size),
    var(--default-size),
    var(--default-size),
    var(--default-size);
    
  box-shadow: inset -1vmin 0px 0px 1vmin rgba(235,235,239,.2);
  
}

div::before, div::after {
  content: '';
  position: absolute;
}



/* CSS Transform Animations */
div::before {
  animation: squeeze var(--squeeze-duration) 0ms infinite alternate ease-in-out;
  animation-play-state: var(--squeeze-state, paused);
  transform-origin: left center;
}
div::after {
  animation: go-with-squeeze var(--squeeze-duration) 0ms infinite alternate ease-in-out;
  animation-play-state: var(--squeeze-state, paused);
  will-change: transform;
}
div {
  --extra-animations: note-float 3200ms infinite alternate ease-in-out;
  animation: go-against-squeeze var(--squeeze-duration) 0ms infinite alternate ease-in-out,
    var(--extra-animations);
  animation-play-state: var(--squeeze-state, paused);
  will-change: transform, text-shadow;
  transition: text-shadow 2000ms ease-in-out;
}

.supports-variables-in-keyframes div {
  --extra-animations: 
    press-button1 var(--button-duration, 1000ms) 200ms infinite alternate,
    press-button4 var(--button-duration, 1000ms) 2000ms infinite alternate,
    press-button7 var(--button-duration, 1000ms) -1200ms infinite alternate,
    press-button8 var(--button-duration, 1000ms) 3400ms infinite alternate,
    press-keys var(--keys-duration, 8000ms) 0ms infinite both,
    note-float 3200ms infinite alternate ease-in-out;
}

@keyframes squeeze {
  80%, 0% {
    transform: scaleX(1) translate3d(0,0,0);
  }
  40% {
    transform: scaleX(.8) translate3d(0,0,0);
  }
  100%, 60%, 13% {
    transform: scaleX(.3) translate3d(0,0,0);
  }
}
@keyframes go-with-squeeze {
  80%, 0% {
    transform: translateX(0);
  }
  40% {
    transform: translateX(calc(var(--bellow-width) * -.2));
  }
  100%, 60%, 13% {
    transform: translateX(calc(var(--bellow-width) * -.7));
  }
}
@keyframes go-against-squeeze {
  80%, 0% {
    transform: translateX(calc(var(--bellow-width) * -.66));
  }
  40% {
    transform: translateX(calc(var(--bellow-width) * -.56));
  }
  100%, 60%, 13% {
    transform: translateX(calc(var(--bellow-width) * -.31));
  }
}
@keyframes note-float {
  30% {
    text-shadow: var(--notes-full-2);
  }
  60% {
    text-shadow: var(--notes-full-3);
  }
  100% {
    text-shadow: var(--notes-full-4);
  }
}


@keyframes press-button1 {
  50% {
    --button1-dim: 1.2vmin;
    --button1-color: var(--color1alt);
  }
}
@keyframes press-button4 {
  50% {
    --button4-dim: 1.2vmin;
    --button4-color: var(--color1alt);
  }
}
@keyframes press-button7 {
  50% {
    --button7-dim: 1.2vmin;
    --button7-color: var(--color1alt);
  }
}
@keyframes press-button8 {
  50% {
    --button8-dim: 1.2vmin;
    --button8-color: var(--color1alt);
  }
}
@keyframes press-keys {
  0% {
    --white1: var(--color2alta);
  }
  3% {
    --white1: var(--white);
    --white2: var(--white);
    --black1: var(--color2alt);
  }
  6% {
    --black1: var(--black);
    --black2: var(--black);
    --white2: var(--color2alta);
  }
  9% {
    --white2: var(--white);
    --white3: var(--white);
    --black2: var(--color2alt);
  }
  12% {
    --black2: var(--black);
    --black3: var(--black);
    --white3: var(--color2alta);
  }
  15% {
    --white3: var(--white);
    --white4: var(--white);
    --black3: var(--color2alt);
  }
  18% {
    --black3: var(--black);
    --white5: var(--white);
    --white4: var(--color2alta);
  }
  21% {
    --white4: var(--white);
    --black4: var(--black);
    --white5: var(--color2alta);
  }
  24% {
    --white5: var(--white);
    --white6: var(--white);
    --black4: var(--color2alt);
  }
  27% {
    --black4: var(--black);
    --black5: var(--black);
    --white6: var(--color2alta);
  }
  30% {
    --white6: var(--white);
    --white7: var(--white);
    --black5: var(--color2alt);
  }
  33% {
    --black5: var(--black);
    --white8: var(--white);
    --white7: var(--color2alta);
  }
  36% {
    --black6: var(--black);
    --white7: var(--white);
    --white8: var(--color2alta);
  }
  
  
  39% {
    --white8: var(--white);
    --white9: var(--white);
    --black6: var(--color2alt);
  }
  42% {
    --black6: var(--black);
    --black7: var(--black);
    --white9: var(--color2alta);
  }
  45% {
    --white9: var(--white);
    --white10: var(--white);
    --black7: var(--color2alt);
  }
  48% {
    --black7: var(--black);
    --black8: var(--black);
    --white10: var(--color2alta);
  }
  51% {
    --white10: var(--white);
    --white11: var(--white);
    --black8: var(--color2alt);
  }
  54% {
    --black8: var(--black);
    --white12: var(--white);
    --white11: var(--color2alta);
  }
  57% {
    --white11: var(--white);
    --black9: var(--black);
    --white12: var(--color2alta);
  }
  60% {
    --white12: var(--white);
    --white13: var(--white);
    --black9: var(--color2alt);
  }
  63% {
    --black9: var(--black);
    --black10: var(--black);
    --white13: var(--color2alta);
  }
  66% {
    --white13: var(--white);
    --white14: var(--white);
    --black10: var(--color2alt);
  }
  69% {
    --black10: var(--black);
    --white15: var(--white);
    --white14: var(--color2alta);
  }
  72% {
    --black11: var(--black);
    --white14: var(--white);
    --white15: var(--color2alta);
  }
  
  
  75% {
    --white15: var(--white);
    --white16: var(--white);
    --black11: var(--color2alt);
  }
  78% {
    --black11: var(--black);
    --black12: var(--black);
    --white16: var(--color2alta);
  }
  81% {
    --white16: var(--white);
    --white17: var(--white);
    --black12: var(--color2alt);
  }
  84% {
    --black12: var(--black);
    --black13: var(--black);
    --white17: var(--color2alta);
  }
  87% {
    --white17: var(--white);
    --white18: var(--white);
    --black13: var(--color2alt);
  }
  90% {
    --black13: var(--black);
    --white19: var(--white);
    --white18: var(--color2alta);
  }
  93% {
    --white18: var(--white);
    --black14: var(--black);
    --white19: var(--color2alta);
  }
  96% {
    --white19: var(--white);
    --white20: var(--white);
    --black14: var(--color2alt);
  }
  99% {
    --black14: var(--black);
    --white20: var(--color2alta);
  }
  100% {
    --white20: var(--white);
  }
}











body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  overflow: hidden;
  background: hsl(33, 80%, 49%);
}
form {
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  padding: 1vmin;
  background: hsla(43, 0%, 0%, .4);
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: system-ui, --apple-system, 'Segoe UI', sans-serif;
  color: #fafaff;
}





:root {
  --test-value: 0;
}
@keyframes supportTest {
  100% {
    --test-value: 1;
  }
}
body {
  animation: supportTest 1ms 0ms 1 linear forwards;
}
!

JS 

              
                var div = document.querySelector('div');
var buttons = {};
const newDim = '1.2vmin';
const numBlackKeys = 14;
const numWhiteKeys = 20;
var intervals = [];
var running = true;
var isKeyframesSupported;
//

//check for support of variables in keyframes
setTimeout(function() {
  isKeyframesSupported = getComputedStyle(document.body).getPropertyValue('--test-value').indexOf('1') > -1;
  if (isKeyframesSupported) { //force all browsers to do fallback until  I ahve time to figure out why this check breaks Safari only
    document.documentElement.classList.add('supports-variables-in-keyframes');
  } else {
    //do fallback rAF
    
    startIntervals();
    pressKeys();
  }
  
  
  //Animation Control
  document.getElementById('pauser').addEventListener('click', function(e) {
    if (e.currentTarget.checked) {
      div.style.setProperty('--squeeze-state', 'running');
      running = true;
      if (!isKeyframesSupported) {
        requestAnimationFrame(pressKeys);
        startIntervals();
      }
    } else {
      div.style.setProperty('--squeeze-state', 'paused');
      running = false;
      intervals.forEach(function(interval) {
        clearInterval(interval);
      });
    }
  });
}, 500);





function startIntervals() {
  intervals[0] = setInterval(() => { pressButton(1) }, 900);
  intervals[1] = setInterval(() => { pressButton(4) }, 1200);
  intervals[2] = setInterval(() => { pressButton(7) }, 1600);
  intervals[3] = setInterval(() => { pressButton(8) }, 1700);
}

function pressButton(index) {
  requestAnimationFrame(function() {
    var enabled = !!buttons[index]; 
    div.style.setProperty('--button'+index+'-dim', enabled ? newDim : 'var(--button-dim)');
    div.style.setProperty('--button'+index+'-color', enabled ? 'var(--color1alt)' : 'var(--color1)');
    buttons[index] = !enabled;
  });
}

function pressKeys() {
  var now = Date.now();
  var blackKey = Math.ceil((now % 2800) / 200);
  var whiteKey = Math.ceil(((now + 200) % 3000) / 150);
  div.style.setProperty('--black'+blackKey, 'var(--color2alt)');
  div.style.setProperty('--black'+((blackKey - 1) || numBlackKeys), 'var(--black)');
  div.style.setProperty('--white'+whiteKey, 'var(--color1alta)');
  div.style.setProperty('--white'+((whiteKey - 1) || numWhiteKeys), 'var(--white)');
  //console.log(whiteKey);
  if (running) {
    requestAnimationFrame(pressKeys);
  }
}
!
999px

Console