Combine and Minify Multiple CSS / JS Files
Check out minify - it allows you combine multiple js, css files into one just by stacking them into a url, e.g.
<script src="/scripts/js/main.js,/scripts/js/adapter/adapter.js"></script>We've used it for years and it does a great job and does it on the fly (no need to edit files).
I think the YUI Compressor is the best there is. It minifies JS and CSS and it even strips those console.log statements people use for low-level JavaScript debugging.
You can start it in an ant task and therefore include it into your post/pre-commit hooks if you use svn/git.
UPDATE: Nowadays I use grunt with the concat, minify & uglify contributions. You can use it with a watcher so it creates new minified files in the background whenever you change your source.The uglify contrib not only strips console logs, but it also strips unused functions and properties.
See this tutorial for a brief insight.
UPDATE:Nowadays people step back from grunt und its predecessor "gulp" and use npm as a build tool. Read up on it here.
UPDATE:So now people use yarn to run npm. No wonder; yarns icon is a cat.Most current frameworks use webpack to bundle the resources into packages, which then also takes care of minification.
I'd need to update all pages that needs these 3 files to reference to the newly-minified CSS.
Firstly I would say you should have common header. So it will needn't to change all headers at all time whenever necessary. It's good practice to have single header or 2-3. So as your page need you can change your header. So whenever you want to extend your web-app it will be less risky and tedious.
You havn't mentioned your development environments. You can see there are many compressing tools listed for different environments. And you are using good tool i.e.YUI Compressor.