.square, .circle {
    width: 100px;
    height: 100px;
    display: inline-block;
    float: left;
}
.circle {
    border-radius: 50%;
}
#blockRed {
    background-color: red;
}
#blockYellow {
    background-color: yellow;
}
#blockWood {
    background-image: url('https://img.freepik.com/free-vector/oak-wood-textured-design-background_53876-115928.jpg?size=338&ext=jpg&ga=GA1.1.87170709.1707955200&semt=ais');
    background-size: cover;
    background-position: center center;
}
#container {
    background-color: darkblue;
    margin: 0 auto;
    width: 400px;
    height: 400px;
}