body {
  margin:0;
  background:black;
  overflow:hidden;
}
#sky{
  width:100vw;
  height:100vh;
}
.star{
  width:4px;
  height:4px;
  background:white;
  border-radius:50%;
  position:absolute;
  box-shadow:
    0 0 10px white,
    0 0 20px white,
    0 0 40px white;
  animation:twinkle 2s infinite;
}
@keyframes twinkle{
  0%{
    opacity:0.2;
  }
  50%{
    opacity:1;
  }
  100%{
    opacity:0.2;
  }
}
.star:hover{
  transform:scale(2);
}


.nebula{
  position:absolute;
  width:400px;
  height:400px;
  border-radius:50%;
  filter:blur(100px);
  opacity:0.3;
  
  animation:wave 5s infinite;
}
@keyframes wave{
  0%{
    transform:translateX(0px);
  }
  50%{
    transform:translateX(50px);
  }
  100%{
    transform:translateX(0px);
  }
}
.nebula1{
  background:purple;
  top:100px;
  left:100px;
}
.nebula2{
  background:blue;
  top:300px;
  right:100px;
}