Edit in JSFiddle

<p class="choice">p.choice</p>
<div id="main">
  <p>p</p>
  <div class="choice">div.choice</div>
</div>
<ul>
  <li>list item <span class="choice">span.choice</span> </li>
  <li>list item <span>span</span></li>
</ul>

var choice = document.getElementsByClassName("choice"); // 클래스가 choice인 모든 요소

var len = choice.length
for (var i = 0; i < len; i++) {
  choice[i].style.color = "#FF0000";
}