https://github.com/eea/eea.facetednavigation/blob/master/eea/facetednavigation/profiles/default/cssregistry.xml
<?xml version="1.0"?>
<object name="portal_css" meta_type="Stylesheets Registry">
<stylesheet id="@@faceted_view.css" remove="True" />
<stylesheet id="@@faceted_edit.css" remove="True" />
<stylesheet title="Faceted View CSS" cacheable="True" compression="none"
cookable="True" enabled="on" expression=""
id="faceted_view.css" media="all" rel="stylesheet" rendering="import"/>
<stylesheet title="Faceted Edit CSS" cacheable="True" compression="none"
cookable="True" enabled="on"
expression="python:'configure_faceted.html' in request.URL0"
id="faceted_edit.css" media="all" rel="stylesheet" rendering="import"/>
</object>
Why import instead of link and compressione none? It dates from 2009, is
still valid now? import should be worst for performaces, plus Plone
portal_css merging interrupts.
http://lmgtfy.com/?q=css+import+performance