textarea#src,
textarea#dest {
  resize: both;

  padding: 0.5em;
}

div#buttons {
  margin-top: 1em;
  margin-bottom: 1em;

  display: flex;
  justify-content: center;
  align-items: center;
}

button#decode {
  margin-left: 1em;
}

.error {
  color: red;
}

div#buttons,
textarea#src,
textarea#dest {
  width: 350px;
  box-sizing: border-box;
}