Custom elements in chart

Hi just a general question regarding adding custom lines and things of the sort to a plotly graph…
If i had for example two traces plotted on the same chart, each of which creates a line, would it be possible to create a vertical line that is connected to both of the line plots and shows something like a ‘difference’ between them? Is it possible to add this kind of customizations on top of a plotly graph or am i better off creating this from scratch in d3??

thank you

line chart reference here:

Probably doable using