How is height in Tab1...Tab4 controlled?

I have four tabs, each with the same size background image. The tab labels are changing position when clicked; what would be your suggestion to keep them pinned to the same position when the 'slide' is changed?

dev url: http://goo.gl/Txyc7b

Hi

Best would be to set a min-height, which would be the height of the biggest background image, in css, but for that I would need to see Your site first. I've tried the link, but it's protected by password.