center a div or an element inside absolute div

how to center an element inside a div that uses position absolute and width percentage

by heriberto perez

HTML

<div class="container"><p>Donec ullamcorper nulla non metus auctor fringilla. Maecenas faucibus mollis interdum. Sed posuere consectetur est at lobortis. Vivamus sagittis lacus vel augue laoreet rutrum faucibus dolor auctor. Sed posuere consectetur est at lobortis.</p></div>

CSS

.container
{
  position: absolute;
  top: 15px;
  z-index: 2;
  background: yellow;
  width:40%;
  background: #fff;
  margin: 0 auto;
  left:0;
  right:0;
}