title: Do additional, unused CSS definitions slow down browsers?
body: <p>After working with many CMSes and cutting up many HTML designs, when I saw <a href="http://silverstripe.com/" rel="noreferrer">SilverStripe's use of CSS</a>, I was converted.</p>
  
  <p>Essentially, that it would be a waste to change IDs in <code>&lt;div&gt;</code> tags depending upon the page you were on, and that changing the <code>&lt;body&gt;</code> tag's classes and ID would be an easier way of changing specific pages.</p>
  
  <p>Such convictions were brought into question by a coworker during the following problem:</p>
  
  <p>On a specific website, we have a variety of pages that are similar in structure.  Some may include a special form, and some may not.  All special forms should have a different background image depending upon the sub-section we are in.</p>
  
  <p>Due to a claim that "additional lines of CSS slow down <code>body.onLoad</code>s," my argument to code all background expectations in the CSS was rejected.</p>
  
  <p>Can anybody cite evidence between a variety of cases?  Cases including: Badly-coded CSS, and CSS well-coded, but having a variety of unused CSS on each page?</p>
  
  <blockquote>(And specifically speaking on my problem, can anybody explain my unease?  I feel uncomfortable assuming images will be there and auto-generating Inline CSS (or header-section-based style tags) based upon a variable from a database.)</blockquote>