I want to center my content horizontally

Depending on what you want to center there are 2 easy ways of doing it.

if you are trying to center an inline element or an inline-block element then you give it's parent
text-align:center;

HTML

<div>
  <a href="bob.html">bob</a>
</div>

CSS

div{
text-align:center;
}

if you are trying to center a block element then you give it a width less than 100%, left margin and right margin of auto.

HTML

<div>...</div>

CSS

div{
width: 50%;
margin-left: auto;
margin-right: auto;
}