How to set page height to 100%?

We have switched from TB 2.x to TB 3.x and now I am totally perplexed on how to set the page height of a wiki to 100%. In TB 2.x, there is an option to set the page height to a percentage or a set height, but I cannot find that option in TB 3.x. After upgrading TB, a lot of our old wikis are now broken and look like this.

Is there a way to set the page height to 100% so that the page content doesn't flow off the open of the page? I cant find it! Thanks!