.cube,
.cube * {
  position: absolute;
  top: 50%;
  left: 50%;
}

.cube {
  user-select: none;
  cursor: move;
}

.cube div span {
  position: relative;
  top: 60px;
  left: -5px;
  font-size: 8em;
}

.face {
  box-sizing: border-box;
  border: solid 1px;
  margin: -8em;
  width: 16em;
  height: 16em;
  box-shadow: inset 0 0 15px rgba(0, 0, 255, 0.6);
  text-align: center;
  /** backface-visibility: hidden; /**/
}

.face:nth-child(1) {
  background: rgba(255, 0, 0, 0.2);
}

.face:nth-child(2) {
  background: rgba(255, 255, 0, 0.2);
}

.face:nth-child(3) {
  background: rgba(0, 255, 0, 0.2);
}

.face:nth-child(4) {
  background: rgba(0, 255, 255, 0.2);
}

.face:nth-child(5) {
  background: rgba(0, 0, 255, 0.2);
}

.face:nth-child(6) {
  background: rgba(255, 0, 255, 0.2);
}