class.mold
From Documentation
class.mold
Default: none [Since 5.0.0]
It specified the default mold of the specified component. The property name is a concatenation of the class name of the component and mold. For example, the property for the button's default mold is called org.zkoss.zul.Button.mold.
<library-property>
<name>org.zkoss.zul.Button.mold</name>
<value>trendy</value>
</library-property>