I have been assigned a task for my college - I study philology - to write a simple website. I thought it easy, because I am also a IT technician (but I am not so good with computers, that's why I have chosen language and literature instead of computing). We have to create a website about our habits related to Internet browsing.

I created a website in pure HTML and CSS, have chosen colors, names of divs etc. You know, regular stuff.

The problem is with my sidebar. I clearly stated in CSS that "height: 100%", however, it ends abruptly in the middle of the website and for no reason known to me.

The code is on Github: https://github.com/SzymonBrycki/EnglishWebpage

I asked on one Polish webforum, but got a really bief, yet complicated response. Something about... calc? I looked it on the WWW3 Schools websites, but could not understand what it was about.

Could someone please explain to me in simple words what I should do to make my sidebar whole-site long?