I need to make a really complicated diagram for a website, in which the hierarchy will be a bit messy: arrows will go up and down, sometimes an element will point to several others, and sometimes there will be several elements pointing to the same one. I have found this method, but it doesn't allow more than one parent for an element and therefore won't do the trick in this case.
It has to be done in HTML/CSS, because my intention is to add some Javascript to change the content of the blocks dinamically.
This is an example of the level of complexity I need to achieve:
You might want to take a look at this