Steps to Reproduce

http://zkfiddle.org/sample/1ctn80m/1-tabpanel-is-squeezed-by-tabs-when-tabbox-width-is-not-enough
run the fiddle with iceblue theme and ZK8.5.0 or a later version.

Current Result

tabpanel is squeezed by tabs

Expected Result

tabs shouldn't warp and press the tabpanel

Debug Info

https://github.com/zkoss/zk/blob/72c5cfad4fd757ef9851e74fe074b9250cff16e8/zul/src/archive/web/js/zul/tab/Tabs.js#L208
tabsOffsetWidth become 0 when using iceblue
then this._showbutton(true); take off the height from tabs
this may help