JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdn.jsdelivr.net/jquery/2.2.4/jquery.min.js"></script>
<body>
  <div id="one">
  </div>
  <div id="two">
  </div>
</body>

CSS

body {
  margin: 20px;
}
#one {
  max-width: 100%;
  background-color: aqua;
  height: 300px;
}
#two {
  border-top: 100px solid red;
  border-right: 250px solid transparent;
  border-bottom: 100px solid transparent;
  border-left: 250px solid transparent;
  width: 0;
  height: 0;
}

JavaScript

$(window).resize(function () {
  var divWidth = $('#one').width();
	$('#two').css({
    borderLeftWidth: divWidth / 2,
    borderRightWidth: divWidth / 2
  })
});

$(window).trigger('resize');