写一个动画，向上匀速移动100px，向下以1.5倍速度移动200px，一直反复循环

    .animation-block {        width: 50px;        height: 50px;        background: red;        margin-top: 200px;        animation: up 1s linear, down 1.5s linear 1s;    }    @keyframes up {        0% { transform: translateY(0px);        }        50% { transform: translateY(-100px);        }        100% { transform: translateY(0px);        }    }    @keyframes down {        0% { transform: translateY(0px);        }        50% { transform: translateY(100px);        }        100% { transform: translateY(0px);        }    }<div ></div>var box = document.querySelector('.animation-block');var i = 0box.addEventListener("webkitAnimationEnd", function() {      i++    if (i == 2) {        i = 0        box.classList.remove('animation-block');        setTimeout(function() { box.classList.add('animation-block');        }, 0)    }}, false);