html, body {
  height: 100%;
  margin: 0;
  padding: 0;
  overflow: hidden; /* 禁止出现滚动条 */
}

#app {
  height: 100%;
  width: 100%;
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

#app > * {
  flex: 1 1 auto;
  overflow: hidden;
}