JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrap">
  <div class="a"></div>
  <div class="b"></div>
</div>

SCSS

.wrap {
  height: 500px;
  background: #000;
  position: relative;
}

.a, .b {
  height: 50px;
  width: 25px;
  background: red;
  position: absolute;
}

.a {
  bottom: 100px;
  left: 50px;
  
  &:after {
    content: '';
    right: 50%;
    bottom: 100%;
    height: 500px;
    width: 1px;
    background: blue;
    position: absolute;
  }
}

.b {
  bottom: 350px;
  left: 330px;
}

JavaScript

let bt = parseInt ($('.b').css('bottom'));
let lf = parseInt($('.b').css('left'));

let a = {l: 50, b: 100 };
let b = {l: lf, b: bt};

t = {
	a: a.l - b.l,
  b: a.b - b.b,
  c: 0
};

t.c = Math.sqrt(t.a*t.a + t.b*t.b);
let cos = Math.acos(t.a / t.c) / Math.PI * 180;
cos = cos-90;
$('.a').css({ transform: 'rotate(' + cos + 'deg)'});