03.css

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html,
body {
    width: 100%;
    height: 100%;
    background-color: #dadada;
    overflow: hidden;
}

main {
    width: 100%;
    height: 100%;
    background-color: #37212D;
    display: flex;
    align-items: center;
    justify-content: center;
}

#box{
    width: 700px;
    height: 400px;
    background-color: #ffffff;
    display: flex;
    position: relative;
    overflow: hidden;
}

#left{
    width: 50%;
    height: 100%;
    background-color: #76608A;
    position: relative;
    overflow: hidden;
}

#left::before{
    content: '';
    width: 100%;
    height: 80%;
    overflow: hidden;
    background-color: #BCE6E9;
    z-index: 10;
    border-radius: 50%;
    top: 60%;
    position: absolute;
}

#box::before{
    content: '';
    width: 100%;
    height: 200%;
    overflow: hidden;
    background-color: #EE9B99;
    z-index: 2;
    border-radius: 50%;
    position: absolute;
}

#right{
    width: 50%;
    height: 100%;
    background-color: #EE9B99;
    position: relative;
    z-index: 3;
    overflow: hidden;
}

#right::before{
    content: '';
    width: 100%;
    height: 100%;
    overflow: hidden;
    background-color: #76608A;
    z-index: 10;
    border-radius: 50%;
    right: 50%;
    position: absolute;
}

#right::after{
    content: '';
    width: 200%;
    height: 200%;
    overflow: hidden;
    background-color: #BCE6E9;
    z-index: 7;
    right: 9%;
    border-radius: 50%;
    position: absolute;
}



@media (max-width:720px) {
    #box{
        width: 600px;
        height: 325px;
    }
}

@media (max-width:550px) {
    #box{
        width: 450px;
        height: 225px;
    }
}