.ChatShell {
  display: flex;
  height: inherit;
  overflow: hidden;
  width: 100%;
  > div:first-of-type {
    width: 530px;
  }
  > div:nth-of-type(2) {
    flex: 3;
  }
}

@media (max-width: 768px) {
  .ChatShell {
    > div:first-of-type {
      width: 100%;
    }
  }
}