How do you make a long screenshot image block scrollable?

I want to add a full page screenshot on my portfolio. I want it to have a set height, but be scrollable within those set dimensions. I've tried the other methods on previous posts, but they did not work. 

Use a code block. Add the image to the code block '<img src="your_link_here".../>'

Set the dimensions of the image as a pixel-based unit.

Set the maximum height or hard-code the height of the code block to your desired dimension.

You should now be able to leverage the 'overflow' CSS property to achieve your desired outcome 😄