<div class="container">
    <div class="box"></div>
</div>

.container{
    width:640px;
    height:360px;
    background:#ff0000;
    position:relative;
    overflow:hidden;
}

.container .box{
    width:50px;
    height:50px;
    left:50px;
    top:50px;
    position:absolute;
    background:#0000ff;
    cursor:move;
}