Often when I\'m designing a site, I have a need for a specific style to apply to a specific element on a page and I\'m absolutely certain it will only ever apply to that element
Look to see if there's a combination of classes which would give you the result that you want. You might also want to consider breaking up the CSS for that one element into a few classes that could be re-used on other elements. This would help minimize the CSS required for your site as a whole.
I would try to avoid page-specific CSS at the top the HTML files since that leaves your CSS fragmented in the event that you want to change the appearance of the site.
For CSS which is really, truely, never to be used on anything else, I would still resort to putting a #id
rule in the site-wide CSS.
Since the CSS is linked in from a different file it allows the browsers to cache that file, which reduces your server bandwidth (very) slightly for future loads.