No background color at bottom of short pages

On short pages the body content color ends at the bottom of the last line of text (or other content). Below is only a white space. I thougth it must be the background color, but I can chnge the background in the theme options to whatever I want, it stays white.

You can see it here:
https://www.naenikon.ch/2014/gemeindeverein/kontakt/

Any idea how to fix this?