Heights

HTML

<div class="features a"></div>
<div class="features b"></div>
<div class="features c"></div>

CSS

.a { height: 30px; background-color: red; }
.b { height: 120px; background-color: aqua; }
.c { height: 50px; background-color: blue; }

JavaScript

var elements = document.getElementsByClassName('features');

var elementHeights = Array.prototype.map.call(elements, (el) => {
  return el.clientHeight;
});

var maxHeight = Math.max(...elementHeights)

Array.prototype.forEach.call(elements, (el) => el.style.height = `${maxHeight}px`);