How do I vertically center align the parent container to the canvas which has position:relative? The parent container has a child element with
One solution is to wrap your .container with two wrappers; give the first one display: table; and height: 100%; width: 100%; and the second display: table-cell; and vertical-align: middle;. Also make sure your body and html have full height.
Here's a little working demo: little link.
Another method is to apply top: 50%; to your .container and margin-top: -150px; (300px / 2 = 150px). (Note that this method requires you to know the exact height of your container, so it might not be exactly what you want, but it might as well be!). A little working demo of this latter method: another little link.
I hope that helped!