Your css file should be in the theme css folder and not called in 'page_theme.php'. Call your css from the 'header.php' file, example:

Hey Steevb,

I do have my css file in the theme folder, only the Concrete5 system is also using this css file.

When I make a global change, for example: a{ color: red;} not only the theme links turn red but also the concrete5 system links turn red.

Thanks for your reply, I appreciate your help!

So are you 'wrapping' your theme, so it does not to interfere with C5?

I would like to see a live site or your theme package to help more.

Hey Steevb,

Thanks for your reply!

I saw you mentioned .less and .less is a new for me so I was searching on they internet for some tutorials.
If I am right this is something that has to be installed right?
Is this preinstalled in Concrete5.7?

@nesoor

I recommend reading about scoping your theme CSS with .ccm-page.
http://www.concrete5.org/community/forums/5-7-discussion/less-and-c...
http://www.concrete5.org/documentation/how-tos/designers/easily-sco...

Currently you are writing "global" CSS styles. They affect everything on your site - your theme and the concrete5 UI. Scoping your CSS will let you target just your theme.

Less is a CSS preprocessor. It adds useful extra features to CSS that makes writing CSS faster and easier to maintain. Concrete5 comes with a Less compiler.

http://lesscss.org/