owl/examples/demo/app.css

.main {
  position: absolute;
  left: 0;
  right: 0;
  top: 0;
  bottom: 0;

  display: grid;
  grid-template-columns: 200px 1fr;
}

.left-thing {
  background-color: gray;
  padding: 20px;
}

.left-thing button {
  width: 100%;
}

.right-thing {
  padding: 20px;
  overflow: auto;
}

/* Message widget */
.message .author {
  font-weight: bold;
}

.message {
  width: 400px;
  background-color: lightblue;
  margin: 10px 5px;
  border-radius: 5px;
  padding: 5px;
}