// 摆动
.animate-swing(@animation_name: animation-swing, @duration: 1s, @loop: infinite) {
    .animation(@animation_name @duration @loop);

    & when (@prefix = true) {
        @-webkit-keyframes @animation_name { .keyframes('-webkit-'); }
        @-moz-keyframes @animation_name { .keyframes('-moz-'); }
    }

    @keyframes @animation_name { .keyframes; }

    .keyframes(@prefix: '') {
        @pf: e('@{prefix}');
        20%,40%,60%,80%,100% { @{pf}transform-origin: top center; }
        20% { @{pf}transform: rotate(15deg); }
        40% { @{pf}transform: rotate(-10deg); }
        60% { @{pf}transform: rotate(5deg); }
        80% { @{pf}transform: rotate(-5deg); }
        100% { @{pf}transform: rotate(0deg); }
    }
}