how to make a button active by default code example

Example: how to make a button active by default

<div id="myDIV">
  <button class="btn">1</button>
  <button class="btn active">2</button>
  <button class="btn">3</button>
  <button class="btn">4</button>
  <button class="btn">5</button>
</div>


style:-
.btn {
  border: none;
  outline: none;
  padding: 10px 16px;
  background-color: #f1f1f1;
  cursor: pointer;
}

/* Style the active class (and buttons on mouse-over) */
.active, .btn:hover {
  background-color: #666;
  color: white;
}