JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
  <div class="text">This is a text that is supposed to get truncated properly when needed.</div>
  <div class="box">Hello</div>
</div>

CSS

.container .box {
  background-color: #efefef;
  padding: 5px;
  border: 1px solid #666666;
  flex: 0 0 auto;
}

.container .text {
  flex: 1 1 auto;
  white-space: nowrap;
  /* overflow: hidden;     REMOVED */
  text-overflow: ellipsis;
}

.container {
  display: flex;
}