style.css

:root {
  --speed: 5;
}

body {
  background-color: lightgreen;
}

.machine {
  background-color: lightcoral;
  border: dashed lightsalmon 3px;
  height: 300px;
  width: 900px;
  margin: auto;
  margin-top: 10%;

  display: flex;
}

#inpSpeed {
  text-align: center;
  font-size: 20pt;
  width: 50px;

  margin-left: 630px;
}

.slot {
  height: 250px;
  width: 250px;
  margin: 20px;

  overflow: hidden;

  background-color: lightslategrey;
  border: solid lightseagreen;

  text-align: center;
  font-size: 100pt;
  line-height: 250px;
}

.slot .value {
  display: inline-block;
  animation-name: slotspin;
  animation-iteration-count: infinite;
  animation-duration: calc(1s / var(--speed));
}

@keyframes slotspin {
  0% {
    transform: translateY(-200px);
  }

  100% {
    transform: translateY(250px);
  }
}