react/example/src/App.css

.app {
  width: 100%;
}
.container {
  display: flex;
  flex-direction: column;
  margin-left: auto;
  margin-right: auto;
  max-width: 860px;
}

.container div {
  display: flex;
  padding: 10px;
  margin-bottom: 10px;
}