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

.container {
    height: 100vh;

    display: flex;
    justify-content: center;
    align-items: center;
}

.square {
    max-width: 600px;
    position: relative;
    width: 500px;
    height: 250px;
    background: green;
    border: 1px solid green;
}

.square__circle {
    position: absolute;
    top: 50%;
    left: 50%;
    background-color: red;
    width: 180px;
    height: 180px;
    border-radius: 50%;

    transform: translate(-50%, -50%);
}

@media (max-width: 480px) {

    .square {
        width: 300px;
        height: 180px;
    }

    .square__circle {
        width: 100px;
        height: 100px;
    }
}