body {
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  background: #eee;
  font-family: sans-serif;
}

#container {
  display: flex;
  flex-direction: column;
  align-items: center;
  max-width: 500px;
  margin: 0 auto;
}

canvas {
  border: 2px solid black;
  margin-bottom: 20px;
  max-width: 100%;
  height: auto;
}

#lower {
  display: flex;
  flex-direction: row;
  justify-content: space-around;
  width: 100%;
}

#buttons {
  display: flex;
  flex-direction: row;
  justify-content: center;
  width: 100%;
  margin-bottom: 10px;
}

#buttons button {
  margin: 0 5px;
}

#instructions {
  width: 50%;
}

#number-pad {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 5px;
  margin-top: 20px;
}

#number-pad button {
  width: 50px;
  height: 50px;
  font-size: 20px;
}

#check-result {
  height: 1.2em; /* Reserve space for the message */
  margin-bottom: 10px;
  visibility: hidden;
}

#check-result.visible {
  visibility: visible;
}