h.css

*{
    margin: 0px;
    padding: 0px;
}

body{
    background-color: plum;

    /* 弹性盒子模型将整个心放在中间 */
    display: flex;
    flex-direction: row;
    align-items: center;
    justify-content:center;
}

html, body{
    /* 让容器的宽度、高度均撑满100% */
    width: 100%;
    height: 100%;
}

.heart{
    width: 200px;
    height: 200px;
    background-color: red;
    position: relative;

    transform: rotate(45deg);

    /* 加入动画内容 */
    animation: heartbeat 0.5s alternate infinite; 
    box-shadow: 0px 0px 30px red;
}

.heart::before{
    content: "";
    width: 200px;
    height: 100px;
    background-color: red;
    position: absolute;
    left: 0;
    top: -99px;

    border-top-left-radius: 100px;
    border-top-right-radius: 100px;
}

.heart::after{
    content: "";
    width: 100px;
    height: 200px;
    background-color: red;
    position: absolute;
    left: -99px;

    border-top-left-radius: 100px;
    border-bottom-left-radius: 100px;
}

/* 实现动画 */
@keyframes heartbeat{
    0%{
        transform: rotate(45deg) scale(0.6);
    }
    100%{
        transform: rotate(45deg) scale(1.4);
    }
}