What effect does a space have before the class name? <p>My aim is to have this class apply only when set on <code>&lt;img&gt;</code> tags. It only works when there is no space between the tag name and the class name, but doesn't when there is. I have seen style sheets with spaces in the signature, so I'm sure it must be valid in some contexts.</p> <p>What is the difference between:</p> <pre><code>img.approved-photo { // no space } </code></pre> <p>and</p> <pre><code>img .approved-photo { // has a space } </code></pre>