JSFiddle - React, Tailwind, and code Playground

HTML

<div class="dm3">
  DM3
</div>


<div class="dm1">
  DM1
</div>

CSS

.dm3 {
  width: 200px;
  background: blue;
}

.dm1 {
  background: green;
  width: 100px;
}

@media only screen and (max-width: 400px) {
  .dm3 {
    width: 400px;
  }
}

JavaScript

$(window).on('load resize', function() { // On load or window resize
  var dm3Width = $('.dm3').width() // Get dm3 width
  $('.dm1').width(dm3Width); // Make dm1 width match dm3 width
});