Current CSS within your product descriptions
Click for preview 
<style><!--
 #header {
 background-color:#0B5694;
 color:white;
 text-align:center;
 padding:5px;
 }
 #nav {
 line-height:30px;
 background-color:#eeeeee;

 width:400px;
 float:left;
 padding:5px;
 }
 #section {
 width:370px;
 float:left;
 padding:10px;
 }
 #footer {
 background-color:#0B5694;
 color:white;
 clear:both;
 text-align:center;
 padding:5px;
--></style>
Updated Product Description CSS
This is the CSS I've applied globally, however, if you were to replace the existing CSS with the following code within the long description of every product, the preview would look correct.
Click for preview 

Code that would need to be replaced.

<style>
.pro-header {
  background-color: #0B5694;
  text-align: center;
  padding: 5px }

.pro-header h1 {
  color: #fff !important }

.pro-nav {
  background-color: #eeeeee;
  width: 400px;
  float: left;
  padding: 5px }
 
.pro-section {
 width: 370px;
 float: left;
 padding: 10px }
 
.pro-footer {
 background-color: #0B5694;
 color: #fff;
 clear: both;
 text-align: center;
 padding: 5px }
</style>
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