Steps to Reproduce

<button label="long operation"  onClick="org.zkoss.lang.Threads.sleep(3000)"/>

zk.xml

    <library-property>
        <name>org.zkoss.zul.progressbox.position</name>
        <value>center, center</value>
    </library-property>

1. embeds the zul with zk js embedded API
2. click the button to show "processing" message
   (reproduce it with https://github.com/zkoss-demo/zkembedded-demo/)

Current Result

on the left, top corner (as the default setting)

Expected Result

at the center of the page because of the specified library property

Debug Information

• if you visit the zul directly (not from the page that embeds the zul), the processing message displays
• need to check other similar library properties that could also fails under embedded case

Workaround

.z-loading