body {
  width: 90%;
  text-align: center;
  font-size: large;
  background-image: url(flow.jpg);
  background-size: cover;
  background-repeat: no-repeat;
}

.code {
  background-color: greenyellow;
  width: 8em;
  height: 200;
  font-size: xx-large;
}

.cent {
  margin-left: auto;
  margin-right: auto;
}

.left {
  text-align: left;
}

.txta {
  height: 2em;
  width: 40em;
  font-size: medium';
}

.bttn {
  font-size: x-large;
}

.chkb {
  height: 40px;
  width: 40px;
}