<div id="container">
                                <div id="header">
                                    <h1>Update here</h1>
                                    <div id="login">
                                        <form action="">
                                          ...
                                        </form>
                                    </div>
                                </div>
                            </div>

#container {
  position: relative;
}



#login {
  position: absolute;
  top: 0;
  right: 10px; 
    background: greenyellow;
  padding: 5px;
  -moz-border-radius: 4px;
  width: 255px;
}

#login form {
  margin-top: 10px;
   position: relative;
   z-index: 10;
}

#login form label, #login form input {
  display: block;

}

#login form button {
  float: right;
  margin-top: 10px;
}

#login a {
  display: block;
  text-decoration: none;
  font-size: 130%;
  font-weight: bold;
  height: 20px;
  padding: 0 20px 0 5px;
  background: url(images/links.png);
  background-position: right -20px;
  background-repeat: no-repeat;
}

#login a.active {
  background-position: right 0;
}