.hidden {
  display: none;
}
body {
  margin: 0;
  width: 100%;
  box-sizing: border-box;
}
#content {
  margin: auto;
  max-width: 60rem;
  padding: 1rem;
}
img {
  width: 40%;
}
canvas {
  width: 100%;
  border: solid 0.1rem #333;
  box-sizing: border-box;
}
.invalid {
  background-color: #faa;
}
.circuit_a {
  padding: 0.5em;
  border: solid 0.3rem #0a0;
  border-radius: 1rem;
}