Why is my <div> not scrolling when it becoms too big?

Yes, this might be the most newbie question out there, but I still have it:

I have a div, which I gave a gray background, just to show you what it affected.

This is the simple class to it:

.test{
    overflow: scroll;
    background-color: gray;
}

And this is what that looks like:

You can clearly see, the divs background is all gray and therefore, when I expand one of the categories, should scroll:

But you also see, that once I expand it to just to be longer than the window, there is no way to scroll, there are no scrollbars – nothing.

But you also see that the div is expaning, as you can see the gray background at the bottom of this picture still. So there is a lot more content after.
If I increase the size of the window, I get to see whats under that, so it does deffinately exist.

Can you give me an example of what else I could try, or what else could be blocking my scroll?

>Solution :

You need to add height to the div, If the div exeeds the height mentioned, It will start scrolling

.test{
    overflow-y: auto;
    background-color: gray;
    height: "80vh"
}