/*
document.getElementById('id1').style.color = "pink";
*/
<div class="">
<h1 id="id1" class="class1 class2" style=""><span>My Heading<span></h1>
</div>
div { margin: 10px; padding: 40px; border: 5px solid red; width: 400px; margin: 0 auto; }
/*
#id1 { color: blue; }
*/
.class2.class2 { color: green; }
.class1 { color: red; }
h1 { color: black; margin: 0 90px; }