How to match height of floating sibling divs

Question

I have the following situation: http://jsfiddle.net/F3SqM/2/

I have two columns, I only know of the height of columnB. Both columns are floating, and I want columnA to m

Answer 1

You can use javascript to change the height of any other object, but you can't use CSS alone.

You say the height of B is dynamic, but without your code it's a bit hard to see why it can be dynamic and how I could write the js code for you.