Untitled

body {
height: 100%;
width: 100%;
margin: 0;
padding: 0;
overflow: hidden;
    background-image:url("bg_beach.jpg");
    background-size: 100% 100%;
    background-attachment: fixed;
    background-repeat: no-repeat;
}

.mydiv {
    position: absolute;
    top: 0;
    left: 0;
    bottom: 0;
    right: 0;
    background-image:url("bg_beach.jpg");
    background-size: 100% 100%;
    background-attachment: fixed;
    background-repeat: no-repeat;
}

#main {
    position: relative;
}

<body>
    <div class="mydiv"></div>
    <div id="main">
        <!-- page content here -->
    </div>
</body>