body {
  background: #cdd0e0;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  font-family: sans-serif;
}

.container {
  background: #1e1e1e;
  padding: 10px;
  border: 4px solid #999;
  border-radius: 4px;
  width: 260px;
}

.display {
  background: #000;
  color: #fff;
  font-size: 2rem;
  text-align: right;
  padding: 15px;
  border-bottom: 4px solid #1e1e1e;
  overflow: hidden;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 4px;
  margin-top: 8px;
}

button {
  background: #555;
  color: #fff;
  border: none;
  padding: 20px;
  font-size: 1.2rem;
  cursor: pointer;
}

button:hover {
  opacity: 0.85;
}

.red {
  background: #a33;
  grid-column: span 2;
}

.blue {
  background: #024;
  grid-row: span 2;
}

.zero {
  grid-column: span 2;
}