trying to get my footer under the last post ? (page height issue)

Hi,

Im trying to make my page height relevant to the content on my page.

But my php / html doesnt recognize my wordpress posts are there, so right now I have set a page height in my style sheet so all the pages are the same length. But some posts have short content, so i have lots of blank space at the bottom and if i have a lot of content, it runs over my footer at the bottom of the page.

How does normal blogs work? Is it code to make the page footer sit under the last post? How to you make them recognize each other?

Here is the link to my site https://www.flexhk.com

Your help would be very much appreciated as always! Thanks