Definition of the problem
there is an area (e.g. <div>) with known height in the page
an internal object (typically long text in <div>) is inside the area and I don't know its height (e.g. because its content is dynamically generated from a database)
I want to center the object vertically within the area
without using HTML tables.

http://www.jakpsatweb.cz/css/css-vertical-center-solution.html