vBulletin Manual - Store CSS as Files

A complex CSS stylesheet can occupy quite a block of text when printed out in full. This entire block of CSS code must be included with every page viewed by your visitors, and with a lot of visitors over a long period of time this can mount up.

One of the beauties of CSS is that the stylesheet can be held in a separate file from the HTML content, allowing web browsers to store the CSS in their cache, negating the need to reload the stylesheet with every page viewed.

vBulletin allows you to have your stylesheets automatically saved to files by the system, resulting in lower bandwidth usage and faster-loading pages for your visitors.

To enable vBulletin to save your stylesheets as files, you must first ensure that your web server has permission to write and delete files within the clientscript/vbulletin_css directory.

You should then go to vBulletin Options > Style & Language Settings and switch the Store CSS Stylesheets as Files? setting to Yes.

After pressing the [Save], your stylesheets will be converted to files and saved into the clientscript/vbulletin_css directory.

Whenever you make a change to your styles that alters the CSS, the stored files will automatically be updated.