css - How do I vertically center align a position:relative element?

Question

How do I vertically center align the parent container to the canvas which has position:relative? The parent container has a child element with position:absolute. The child element has been positioned in the center of the parent container.

Here's a snippet:

.container {
  position: relative;
  width: 300px;
  height: 300px;
  background-color: red;
  margin: auto;
}

.item {
  position: absolute;
  width: 100px;
  height: 100px;
  background-color: blue;
  left: 0;
  right: 0;
  top: 0;
  bottom: 0;
  margin: auto;
}

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

Answer 1

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!