how to make a container to align center code example

Example 1: how to assign something in center inside a div

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

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

P { text-align: center }
H2 { text-align: center }