For example,

<?xml version="1.0"?>
<zk>
<hbox width="300px">
<listbox width="200px" height="200px">
<listitem>
<listcell style="white-space: nowrap;"
label="xxxx x xxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxx
xxxxxxxxx xxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxx"/>
</listitem>
</listbox>
<label value="Hi" style="font-size: 16px; font-
weight: bold"/>
</hbox>
</zk>

You should be able to see the horizontal scrollbar.