#player {
    width: 20px;
    height: 20px;
    background-color: red;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    transition: all 0.1s linear;
    border-radius: 10px;
}

#food {
    width: 20px;
    height: 20px;
    background-color: green;
    position: absolute;
}

body {
    background-size: 100% 100%;
}