This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
You should check panelGrid's columnClasses API : Comma-delimited list of CSS style classes that will be applied to the columns of this table. If the number of elements in this list is less than the number of columns specified in the "columns" attribute, no "class" attribute is output for each column greater than the number of elements in the list. You have 3 columns, and only one element in columnClasses.