HTML5で円のアニメーション効果を作成する方法

@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;
    }