Align divs side-by-side (height not fixed)

Hello,
The following problems occur because the height of my container is not pre-determined – it can vary, and is unknown. I have experimented using query to sort out positioning, but there are two reasons I do not wish to use jquery: this layout would be repeated multiple times on a single page, so I am concerned about, one, page loading times, and two, unique ids (if I reference a class or ID, it would occur multiple times on one page).
How can I align two elements side by side? I have a…
Align divs side-by-side (height not fixed)

See original post by Balmoral