css center div
.my-div{
width: 80%;
margin: 10px auto;
/*
margin-left and right right has 'auto' value
meaning that the browser will automatically calculate the remaining space
and give it to the margin.
From the example. 20% remained from 80%
so that our div will have
margin-right: 10%
margin-left: 10%
and it will be centered.
*/
}