JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
  <div class="block">Test block</div>
  <div class="block">Test block</div>
  <div class="block">Test block</div>
  <div class="block">Test block</div>
</div>
<div id="addMore">Add more blocks</div>

CSS

.block {
  border-bottom: 1px solid red;
  counter-increment: block; 
  margin: 20px 0;
  position: relative;
}
.block:after {
  content: " " counter(block);
}
.block:last-child {
    border-bottom: 0;
}

JavaScript

$("#addMore").one("click", function() {
	$("#container").append($("#container").html());
	$(this).remove();
});