Center this, center that

To center:

if...

<div class=section>
<p>This paragraph…</p>
</div>

then...

.section {
text-align: center; /*to center horizontally*/
position: relative     /* to declare the div as container for the any positioned element within */
}
.container p{
   position: absolute; /*to make the element position absolute*/
   top: 50%;     /*to center vertically*/
   transform: translate(0, -50%) /*to move the element up by half*/
}

or

.center {
    margin-left: auto;
    margin-right: auto;
    width: 70%;
    background-color: #666;
}