Calculating the height of a div using line-height

Calculating the height of a div using line-height

Hi, I'm new here. :)
I'm redesigning my portfolio page: marxen.design/test
I want to have an intro <div> filled with ///////////// but I want the <div> to end after the page fold without cutting apart the last text line.

So heres what I've tryed: 
  1. var mathHeight = ((Math.ceil(($(window).height()
            -($(window).width()*0.1)) / $("body").css('line-height')))
            *$("body").css('line-height'));
  2. var introHeight = function(){ $('#intro').height(mathHeight); }; introHeight();

css:

  1. #intro { width: 80vw; height: 66em; margin: 10vw 0 0 10vw; overflow: hidden; overflow-wrap: break-word; background: #eee; }

The div has a margin-top of 10vw. So, what I am trying to do is take the viewport height, subtract 10vw, divide by the line-height, round up and then multiply again by line-height.

What am I doing wrong here?