.container {
  margin: auto;
  width: 50%;
  border: 3px solid green;
  padding: 10px;
}

#btn-check {
  width: 50px;
  margin-left: 120px;
  margin-top: 10px;
  background-color: green;
  color: whitesmoke;
  border-radius: 5px;
}

.output {
  margin: auto;
  width: 50%;
  padding: 10px;
}