For instance on the homepage and our work page we have portfolio thumbnails and when they click on an item it views the single portfolio item, we would like a close (x) button to appear in the top right of the image for the user to be able to return to the original screen/list.
It’s not usually possible. It could be possible with custom development, but this would be outside the scope of support we can offer. You may wish to consult a developer to assist you with this. X is quite extensible with child themes, so there are plenty of possibilities. Thanks for understanding. Take care!