style.scss

$red: #e74c3c;
$whitegrey: #ececec;

body {
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  font-family: 'Boogaloo', cursive;
  flex-direction: column;
}

h1 {
  animation: 2s ease-in-out slideIn;
}
@keyframes slideIn {
  0% {
    transform: translateX(-400%);
  }

  100% {
    transform: translateX(0);
  }
}

.piano {
  width: 400px;
  height: 400px;
  margin: 0 auto;
  position: relative;
  overflow: hidden;
  box-shadow: 0 5px 10px 2px black;
  display: flex;
}

.user-controls {
  width: 450px;
  height: 100px;
  margin: 0 auto;
  display: -webkit-flex;
  display: -moz-flex;
  display: -ms-flex;
  display: -o-flex;
  display: flex;
  justify-content: space-around;
  align-items: center;
}

.strict-mode > button {
  &:hover {
    background: crimson;
  }
}

.scoreboard {
  width: 60px;
  background: #000;
  border-radius: 50%;
  height: 60px;
  display: -webkit-flex;
  display: -moz-flex;
  display: -ms-flex;
  display: -o-flex;
  display: flex;
  justify-content: center;
  align-items: center;
  color: #fff;
  font-size: 2em;
  margin: 5px;
}

.key {
  width: 100px;
  height: 100px;
  min-height: 100%;
  border: 1px solid black;
  position: relative;
  transition: 0.5s ease-in-out;

  &:after {
    width: 50px;
    height: 170px;
    margin-left: 75px;
    overflow: hidden;
    background: #000;
    content: '';
    position: absolute;
    z-index: 3;
    box-shadow: inset 1px 1px 7px 1px #777;
  }
}

.key > p {
  position: absolute;
  bottom: 100px;
  font-size: 3em;
  left: 40%;
}

#b {
  width: 100px;
  height: 100px;
  min-height: 100%;
  border: 1px solid black;
  position: relative;

  &:after {
    opacity: 0;
  }
}

button {
    outline: 0;
    color: #000;
    transition: background 500ms ease-in-out, color 500ms ease-in-out;
    width: 100px;
    height: 40px;
    // height: 100px;
    &:hover {
      color: $whitegrey;
      background: {
        position: 100%;
      }
    }
  }