center an image in a page css code example

Example 1: html center image

/* It's better practice to do this in CSS, not HTML. 
So here is the CSS code! */
img {
  display: block;
  margin-left: auto;
  margin-right: auto;
}

Example 2: position images in center of container

.image-container {
    width: 500px;
    height: 500px;
    position: relative;
}

.image-container img {
    position: absolute;
    right: 0;
    left: 0;
    top: 0;
    bottom: 0;
    margin: auto auto;
}