body {
  background: black;
  color: #00ff00;
  font-family: 'Courier New', monospace;
}
h1 {
  color: #00ff00;
  text-align: center;
}
select, button {
  background-color: black;
  color: white;
  border: 1px solid #00ff00;
  padding: 10px;
  margin: 5px;
}
.matrix {
  width: 80%;
  margin: auto;
  text-align: center;
}
pre {
  background-color: #111;
  padding: 10px;
  border: 1px solid #00ff00;
  text-align: left;
  height: 200px;
  overflow-y: scroll;
}