css3 media

    @media screen and (max- 320px) {
        .cloud{position: fixed;left: 0;top: 70%; 150px;}
        .cloud2{position: fixed;right: 0;top: 30%; 50px;}
        .cloud3{position: fixed;left: 0;top: 23%; 100px;}
    }
    @media screen and (min- 321px) and (max- 375px) {
        .cloud{position: fixed;left: 0;top: 72%; 150px;}
        .cloud2{position: fixed;right: 0;top: 32%; 50px;}
        .cloud3{position: fixed;left: 0;top: 25%; 100px;}
    }
    @media screen and (min- 376px) {
        .cloud{position: fixed;left: 0;top: 68%; 150px;}
        .cloud2{position: fixed;right: 0;top: 32%; 50px;}
        .cloud3{position: fixed;left: 0;top: 25%; 100px;}
    }
    @media screen and (max-height: 480px) {
        .cloud{position: fixed;left: 0;top: 81%; 150px;}
        .cloud2{position: fixed;right: 0;top: 35%; 50px;}
        .cloud3{position: fixed;left: 0;top: 27%; 100px;}
    }