JSFiddle - React, Tailwind, and code Playground

HTML

<p>Change window size to see what will happen with objects</p>

<div>
  <div class="item">Object “A”</div>
  <div class="item">Object “B”</div>
  <span class="item">Object “C”</span>
</div>

CSS

.item { display: block; }
.item:last-child { font-weight: bold; }

@media (max-width: 600px) {
  span.item { display: none; }
  div.item:last-of-type { font-weight: bold; }
}