* {
    padding: 0;
    margin: 0;
}

body {
    /* 弹性布局 页面元素水平+垂直居中 */
    display: flex;
    justify-content: center;
    align-items: center;
    /* 让页面占浏览器总高 */
    height: 100vh;
    background-color: #000;
}

ul {
    /* 相对定位 */
    position: relative;
    display: flex;
    height: 200px;
}

ul::after {
    content: '爱心怦怦跳';
    /* 绝对定位 子绝父相 */
    position: absolute;
    top: 0px;
    left: 50%;
    color: darkturquoise;
    font-size: 30px;
    font-weight: 700;
    /* 上期视频已经讲过了，不明白可以看上期视频 */
    transform: translate(-50%, -600%);
}

li {
    /* 去除项目符号（黑点） */
    list-style: none;
    width: 20px;
    height: 20px;
    border-radius: 10px;
    margin: 0 10px;
}

li:nth-child(1) {
    background-color: red;
    animation: love1 5s 0s infinite;
}

li:nth-child(2) {
    background-color: darkturquoise;
    animation: love2 5s 0.2s infinite;
}

li:nth-child(3) {
    background-color: darksalmon;
    animation: love3 5s 0.4s infinite;
}

li:nth-child(4) {
    background-color: deeppink;
    animation: love4 5s 0.6s infinite;
}

li:nth-child(5) {
    background-color: yellow;
    animation: love5 5s 0.8s infinite;
}

li:nth-child(6) {
    background-color: deeppink;
    animation: love4 5s 1s infinite;

}

li:nth-child(7) {
    background-color: darksalmon;
    animation: love3 5s 1.2s infinite;
}

li:nth-child(8) {
    background-color: darkturquoise;
    animation: love2 5s 1.4s infinite;
}

li:nth-child(9) {
    background-color: red;
    animation: love1 5s 1.6s infinite;
}

@keyframes love1 {

    30%,
    50% {
        height: 60px;
        transform: translateY(-30px);
    }

    70%,
    100% {
        height: 20px;
        transform: translateY(0);
    }
}

@keyframes love2 {

    30%,
    50% {
        height: 125px;
        transform: translateY(-60px);
    }

    70%,
    100% {
        height: 20px;
        transform: translateY(0);
    }
}

@keyframes love3 {

    30%,
    50% {
        height: 160px;
        transform: translateY(-75px);
    }

    70%,
    100% {
        height: 20px;
        transform: translateY(0);
    }
}

@keyframes love4 {

    30%,
    50% {
        height: 180px;
        transform: translateY(-60px);
    }

    70%,
    100% {
        height: 20px;
        transform: translateY(0);
    }
}

@keyframes love5 {

    30%,
    50% {
        height: 200px;
        transform: translateY(-45px);
    }

    70%,
    100% {
        height: 20px;
        transform: translateY(0);
    }
}