Ask the web programmer of your choice about a good IDE for developing CSS, HTML and JS. Most of them will recommend a simple text editor or a tool which is Windows only and not developed for at least 5 years...

Thankfully, I'm not a web programmer, but from time to time, I have my own little share in editing web frontend code. But I don't know CSS by heart. IDEA supports me with auto-complete in CSS files. It marks styles which are used nowhere in HTML.

It even displays a little colored box besides codes like "#628c78". Isn't that a beautiful color? Maybe not. Klick on the box and choose another one. Nice.

Now go to an HTML file, enter... <a class=" ...and invoke auto-complete. Now IDEA shows you a list with all defined CSS styles. Hitting Command-B on a class name brings you directly from HTML to the CSS declaration. That's the 'Integrated' in 'IDE'.