[SalesForce] Import CSS not working in Static Resource

For me works the following code:

background-image: url({!URLFOR($Resource.MyResource,'images/')}myimage.png);

You can't do that with Static Resources but you can achieve dynamic CSS binding with a Visualforce page as external CSS file.

Visualforce page (apex:page) has a content type (contentType) property where you can specify the content type of the file. That means you can render a Visualforce page in different MIME types like JavaScript HTML and CSS etc.

To do that you have to use text/css as contentType of the Visualforce page as below.

Visualforce as external CSS file

<apex:page controller="CssController" contentType="text/css" cache="false" expires="0">
    .classgreen{
        color:{!testColor}
    }
</apex:page>

Visualforce Page where the above file is referenced as CSS file

<apex:page>
  <apex:stylesheet value="{!URLFOR($Page.csspage)}"  />
  <h1 class="classgreen">Congratulations</h1>
  This is your new Page
  <!-- End Default Content REMOVE THIS -->
</apex:page>