*, *::before, *::after {  
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  overflow-x: hidden;
}

.container {
    margin: 200px auto;
    width: 500px;
    height: 300px;
    background-color: green;
    position: relative;
}

.container::before {
    content: '';
    position: absolute;
    width: 180px;
    height: 180px;
    border-radius: 50%;
    background-color: red;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

@media (max-width: 576px) {
    .container::before {
        width: 90px;
        height: 90px;
    }

    .container {
        width: 250px;
        height: 150px;
    }
}