body {
    background-image: url('images/100-1007451_wallpaper-gradient-linear-green-red-green-yellow-red.jpg');
    margin: 0;
    padding: 0
}

@media only screen and (min-width:960px) {
    .deneme {
        width: 500px;
        height: 400px;
        margin: 0 auto;
        margin-top: 30px;
        padding: 20px
    }
}

@media only screen and (min-width:769px) and (max-width:959px) {
    .deneme {
        width: 700px;
        margin: 20px;
        padding: 20px
    }
}

@media only screen and (max-width:768px) {
    .deneme {
        margin: 20px;
        padding: 20px
    }
}