* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
body {
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  background: #050505;
}
.cube {
  position: relative;
  width: 300px;
  height: 300px;
  transform-style: preserve-3d;
  /* 上にボックス足してる */
  transform-style: rotateX(-30deg);
  animation: animate 13s linear infinite;
}
@keyframes animate
{
  0% 
  {
    transform: rotateX(-30deg) rotateY(0deg); 
  }
  100%
  {
    transform: rotateX(-30deg) rotateY(360deg);
  }
}

.cube div {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  transform-style: preserve-3d;
}
.cube div span {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: linear-gradient(#bf0f0f,#00ec00);
  transform: rotateY(calc(90deg * var(--i))) translateZ(180px);
  /* 四隅くっつけるのはこれ↓ 初期値 */
  /* transform: rotateY(calc(90deg * var(--i))) translateZ(150px); */
  /* 300/2=150 */
  opacity: 0.5;
}

.top {
  position: absolute;
  top: 0;
  left: 0;
  width: 300px;
  height: 300px;
  background: rgb(152, 236, 27);
  transform: rotateX(50deg) translateZ(10px);
  /* トップの四角上につけるのこれ↓初期値 */
/*   transform: rotateX(90deg) translateZ(1550px); */
}
.top::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  width: 300px;
  height: 300px;
  background: #0f0;
  transform: translateZ(-380px);
  filter: blur(20px);
  box-shadow: 0 0 120px rgba(0,255,0,0.2),
  0 0 200px rgba(0,255,0,0.4),
  0 0 300px rgba(0,255,0,0.6),
  0 0 400px rgba(0,255,0,0.8),
  0 0 500px rgba(0,255,0,1);
}