<img src="images/circle.png" alt="" id="circle"/>
@mixin ani-btnRotate{
  @keyframes btnRotate{
    from{transform: rotateZ(0);}
    to{transform: rotateZ(360deg);}
  }
}
@include ani-btnRotate;
#circle{
  position: absolute;
  left: 50%;
  width: REM(338);
  height: REM(338);
  margin-top: REM(200);
  margin-left: REM(-338/2);
  transform-origin: center center ;
  animation: btnRotate 1s 1s linear forwards;
  }