JSFiddle - React, Tailwind, and code Playground

HTML

<br><br>

<textarea id=comment>how to position #display always below this text? (even if I press enter)</textarea>

<div id=display></div>

CSS

#display{
  position:absolute;
  border:1px solid #000;
  min-width:100px;
  min-height:100px;
}
#comment{
  width:400px;
  height:200px;
}

JavaScript

var offset = $('#comment').offset();

var x_pos = offset.left;
var y_pos = offset.top;

  $("#display").css({
        top: x_pos,
        left: y_pos
  });