html, body {
  margin: 0;
  padding: 0;
  height: 100%;
  width: 100%;
  font-family: sans-serif;
  background: #111;
  color: #eee;
}
#container {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  height: 100%;
  text-align: center;
}
#stimulusCanvas {
  border: 1px solid #444;
  background: #808080;
}
.hidden {
  display: none;
}
button {
  padding: 10px 20px;
  margin-top: 20px;
  font-size: 16px;
}
label {
  display: block;
  margin-top: 10px;
}