html,
body {
  position: relative;
  width: 100%;
  height: 100%;
}
* {
  -webkit-box-sizing: border-box;
          box-sizing: border-box;
  -webkit-tap-highlight-color: rgba(0, 0, 0, 0);
  margin: 0;
  padding: 0;
  border: none;
}
#app {
  height: 100%;
  display: -webkit-box;
  display: -webkit-flex;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-align: center;
  -webkit-align-items: center;
      -ms-flex-align: center;
          align-items: center;
  -webkit-box-pack: center;
  -webkit-justify-content: center;
      -ms-flex-pack: center;
          justify-content: center;
  font-size: 16px;
  text-align: center;
  color: green;
}