Its due to skin css compression/obfuscation. You can disable this behavior by adding parameter to your web.xml
<context-param>
<description>Disable obfuscation of CSS rules</description>
<param-name>org.apache.myfaces.trinidad.DISABLE_CONTENT_COMPRESSION</param-name>
<param-value>true</param-value>
</context-param>
Although its recommended only for development cycle, so switch it back to false when you go production.