custom.css

@import url("https://fonts.googleapis.com/css?family=Raleway:400,400i,700");

html, body {
  background: linear-gradient(to left, #fd746c , #ff9068);
  height: 100%;
  width: 100%;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  overflow: hidden;
  font-family: Raleway, sans-serif;
}
h1 {
  color: black;
  font-size: 5vw;
  letter-spacing: 6px;
}
.pad {
  width: 400px;
  display: flex;
  justify-content: space-between;
  flex-wrap: wrap;
  padding: 20px 30px;
  background-color: white;
  border: 4px solid black;
  box-shadow: 4px 4px 0 0 black;
}
.key {
  width: 100px;
  height: 100px;
  margin: 10px 0;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  font-size: 20px;
  font-weight: 500;
  color: black;
  background-color: white;
  border: 4px solid black;
  box-shadow: 4px 4px 0 0 black;
  user-select: none;
  transform: translate(0, 0);
}
.sound {
  font-size: 14px;
  text-transform: uppercase;
  color: #ff9068;
  margin-top: 7px
}
.key.playing {
  background-color: #ddd;
  box-shadow: 0 0 0 0 black;
  transform: translate(4px, 4px);
  border-color: #fd746c;
  transition: all 300ms cubic-bezier(0.075, 0.82, 0.165, 1);
}
.key.playing .sound {
  color: #fd746c;
  transform: scale(1.5);
  transition: all 300ms cubic-bezier(0.075, 0.82, 0.165, 1);
}