How does Selenium click on elements that are 50% on screen and 50% not on screen?

There is a div-Element. 50% of its size are on the screen. The other 50% go over the screen height and are not visible. There is no scrolling possible.

I tried to automate a test with Selenium and click on that div-element, but sometimes it works and sometimes it does not.

Why does Selenium not just click on the "on-screen-area" of that div?

And how is this functionality implemented? When I tell Selenium to click on a huge div-element, does it click on a random position on that div?