* {
  margin: 0;
  padding: 0;
}

#container {
  grid-column-gap: 10px;
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  padding: 10px;
}

.text {
  grid-column-start: 1;
  grid-column-end: 3;
  background-color: red;
  /* overflow: hidden; → Firefox needs that. Why? */
}

.horizontal-scroll {
  background-color: green;
  overflow-x: auto;
}

.horizontal-scroll div {
  /* white-space: nowrap; */
  font-size: 30px;
}

<div id="container">
  <div class="text">
    <div>Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea
      takimata sanctus est Lorem ipsum dolor sit amet.</div>
    <div class="horizontal-scroll">
      <div>This container is horizontally scrollable. Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et
        ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet.</div>
    </div>
  </div>
</div>