Drupal employs a great mechanism for speeding up page loads once active development has been completed. Under the Performance settings, there are several options for caching pages, CSS and more. As an example, from a high level, CSS files are consolidated from the often several dozen files down to one, with all whitespace, redundant or superseded selectors and comments removed. This is a great way to speed up your site once you are in Production. If you’re actively developing your site, you don’t want to use this because your changes won’t show reliably without constantly clearing your cache.
There are some caveats though. What? Caveats in Drupal? Uh, yeah. I love Drupal but it has more caveats than the US congress has vacations.
The symptoms are always the same – custom changes (to CSS, for example) don’t show up. In my case, Adaptive Themes manifests this type of behavior. AT has a way of “pre-caching” info within its area of Drupal and this will often lead to CSS customizations not showing up once performance caching has been enabled.
In AT’s case, there is a work around. If changes don’t appear:
- Clear the cache
- Immediately save the AT Theme/Subtheme you are using under Appearance
- Clear the cache again
That should do it. You can read the conversation between some of the AT geniuses here:
https://drupal.org/node/1995938
It’s pretty recent and they will have a solution at some point soon, I hope. Considering how awesome AT is, with all of the Responsive features and easy subtheming, this is a pretty small accommodation to make.
landie.tech 
Hi PJ, in my case I cannot enable css aggregation in my AT subtheme. If I do so I see mobile css mixed with dekstop one …. terrible….
I tried the trick you posted but does not work for me… any other ideas are welcomed 🙂 Thanks. Luigi
P.S.
Great blog…I’ll read it often
LikeLike
hey luigi,
i have had some strange results from aggregation and mobile myself. I use all the mobile css files too so I will have to make this work. i probably won’t get to this today but i will research it and get back to you when i find an answer. no surprise to me that this is not seemless. not much on drupal ever is! if you find an answer, let me know too. thanks for the compliment on the blog. i hope that it helps others!
peej
LikeLike