How Can I Use Two Tags In Same Control

<script>
var myTwoTags = document.getElementsByClassName("className");

function changeColor() {
  myTwoTags.style.color = "#f00"; // red
}
</script>

<button onclick="changeColor()">change color </button>
<h1 class='className'>Change my color</h1>
<p class='className'>Change my color, too</p>

$('className').on("click", function() {
    // Statements
})