Drawing curved SVG arrow lines from div to div

I want to draw two curved arrow lines using SVG to connect two elements to indicate they go back and forth, like this:

I've read a bit about SVG but I'm not totally sure how to create a line that's vertical.

Second, if SVG takes coordinates, do I have to find the coordinate position of the elements before creating the SVG drawing? Does it have to be re-drawn if the window size is adjusted?