CSS divs in php

I am trying to align 2 divs side-by-side within a wrapper div. For some reason the divs are staying left-side on top of right-side.

PHP CODE:

CSS CODE:
#content_wrapper {
width: 980px;
margin-top: 20px;
margin-bottom: 20px;
background-color: #09F;
margin-right: auto;
margin-left: auto;
}
#content_wrapper #left-side {
float: left;
width: 450px;
display: inline;
background-color: #FF9;
}
#content_wrapper #right-side {
float: left;
width: 450px;
display: inline;
background-color: #69F;
}