Big header, scroll down, make header small (Like default size)

Support
9

is there any way to use a parallax background effect for such a header image?

i’ve already tried this code as the css:

.parallax {
    /* The image used */
    background-image: url('img_parallax.jpg');

    /* Full height */
    height: 100%; 

    /* Create the parallax scrolling effect */
    background-attachment: fixed;
    background-position: center;
    background-repeat: no-repeat;
    background-size: cover;
}

and this as the html in the header:

<div class="parallax"></div>

no success, yet.