JSFiddle - React, Tailwind, and code Playground

HTML

<form method="post">
     <button class="btn-small">pew</button>
   <input type="hidden" name="id_add" value="1">
</form>
<form method="post">
     <button class="btn-small">pew</button>
   <input type="hidden" name="id_add" value="2">
</form>
<form method="post">
     <button class="btn-small">pew</button>
   <input type="hidden" name="id_add" value="3">
</form>

<pre id="out"></pre>

CSS

form {
  border: solid 1px gray;
  margin: 1em;
}

.active {
  outline: dashed 2px orange;
}

JavaScript

$('form').submit(function(evt) {
  evt.preventDefault();
  $(this).toggleClass('active');
  
  out.textContent += this.id_add.value;
});