Following way you can put put over canvas using position:absolute;
#header-canvas {
height: 500px;
width: 100%;
}
.login-box {
background: #fff none repeat scroll 0 0;
left: 50%;
padding: 20px;
position: absolute;
top: 50%;
transform: translate(-50%, -50%);
}
<link href="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css" rel="stylesheet"/>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<canvas id="header-canvas" style="background-color:#999"> <header id="header" > </header> </canvas>
<div class="login-box" > <div class="login-box-body">
<form action="" method="post" name="login">
<div class="form-group has-feedback ">
<input type="text" class="form-control" placeholder="Username / Email" required name="login_name"/>
<span class="glyphicon glyphicon-envelope form-control-feedback"></span>
</div>
<div class="form-group has-feedback">
<input type="password" class="form-control" placeholder="Password" name="login_pass"required/>
<span class="glyphicon glyphicon-lock form-control-feedback"></span>
</div>
<div class="row"> <div class="col-xs-4">
<button type="submit" class="btn btn-primary btn-block btn-flat">Sign In</button> </div>
</div>
</form>
</div>
</div>
solved Div over canvas [closed]