The simpler media website CMS
I have seen that in the basic theme two CSS files are linked in the HTML head. One to the themes css and another with the name commons.css. I have not checked, is this in all themes so.
Hint: Put the css from the commons.css in the themes css. This saves a call, which is important for mobile device performance.
Don't worry, it's only a hint.
Comments
This one CSS file is surely not that much of an issue for mobile usage. The common.css is the base css all four personas of the theme share so it is separate.
This could be done via PHP by generating a .css file via PHP. filegetcontent() -> fileputcontent(). Because it is less the traffic, but the call. Every additional call is one too many. Only 1 call is the best.
Find out what Google is planning. That's not funny. For what do I need a ZenPhoto if it is not listed by Google, so no one will find? Private Family Album on the Internet? that's a joke. Google Search Page 1! Otherwise, you can save yourself and spend your time with something else.
Generating CSS via PHP is surely not a great idea. The proper way would be to use a preprocessor like SASS. We might do in the future but for sure not for the basic theme. That is basically dead and does not get any new features.
Google is planning a lot of things and you should be aware of it but not make yourself it's slave.
What does have this to do with the CSS? I do know about request and you surely know that with the next http standard the multiple request issue is not an issue anymore.
Besides this is actual theme territory. You can always create your own.