.grid {
    width : 400px;
    height : 600px;
    background-image: url(img/bg.jpg);
    position: relative;
    margin: auto;
}

.Startbutton {
    background-color: mediumaquamarine;
    width: 200px;
    font-size: 20px;
    padding: 10px;
    border-radius: 5px;
    border: 3px solid yellow;
    color: white;
    text-align: center;
    top : 240px;
    right : 100px;
    position: absolute;
}

.Backbutton {
    background-color: mediumaquamarine;
    width: 200px;
    font-size: 20px;
    padding: 10px;
    border-radius: 5px;
    border: 3px solid yellow;
    color: white;
    text-align: center;
    top : 340px;
    right : 100px;
    position: absolute;
}