CSS设置div高度自动全屏

对body和html都设置高度100%

html,body {
  height: 100%;
  width: 100%;
  margin: 0 0 0 0;
  padding: 0 0 0 0;
  position: relative;
}

然后再对div设置100%

#app {
  height: 100%;
  width: 100%;
  margin: 0 0 0 0;
  padding: 0 0 0 0;
  position: relative;
}