body {
  background: #000;
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100vh;
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}

.calculator {
  width: 320px;
  background: #000;
  border-radius: 40px;
  padding: 20px;
  box-shadow: 0 4px 20px rgba(255,255,255,0.05);
}

.display {
  color: white;
  font-size: 3em;
  text-align: right;
  padding: 20px 10px;
  overflow-x: auto;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
}

.btn {
  height: 70px;
  border: none;
  border-radius: 50%;
  font-size: 1.5em;
  cursor: pointer;
  transition: all 0.1s ease-in-out;
}

.btn:active {
  transform: scale(0.95);
}

.gray {
  background: #a5a5a5;
  color: #000;
}

.dark {
  background: #333333;
  color: #fff;
}

.orange {
  background: #ff9500;
  color: #fff;
}

.zero {
  grid-column: span 2;
  border-radius: 35px;
  text-align: left;
  padding-left: 28px;
}