JSFiddle - React, Tailwind, and code Playground

HTML

<div class="add-html-code test-mar">
  <b>Пример кода:</b>
  <br/>
  <p>1 &lt; 2 + 3 > 4 = 5 : 6 * 7 / 8 \ 9 - 0</p>
  <img class="rounded" src="samples/001_p.jpg" alt="" />
  <img class="rounded-top" src="samples/002_p.jpg" alt="" />
  <img class="rounded-right" src="samples/003_p.jpg" alt="" />
  <img class="rounded-bottom" src="samples/004_p.jpg" alt="" />
  <img class="rounded-left" src="samples/005_p.jpg" alt="" />
  <img class="rounded-circle" src="samples/006_p.jpg" alt="" />
  <img class="rounded-pill" src="samples/007_p.jpg" alt="" />
  <img class="rounded-0" src="samples/008_p.jpg" alt="" />
</div>

<textarea id="out" cols="80" rows="15"></textarea>

JavaScript

out.value = document.querySelector('.test-mar').innerHTML