align center not doing its job code example

Example 1: 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;
}

Example 2: how to assign something in center inside a div

IMG.displayed {
    display: block;
    margin-left: auto;
    margin-right: auto }
...
<IMG class="displayed" src="..." alt="...">