* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  background: #f2f2f2;
  font-family: Arial, sans-serif;
}

.calculator {
  width: 340px;
  background: #1f1f1f;
  border-radius: 24px;
  padding: 20px;
  box-shadow: 0 20px 50px rgba(0, 0, 0, 0.18);
}

.display {
  min-height: 120px;
  padding: 20px 10px;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  align-items: flex-end;
  overflow: hidden;
}

.previous-operation {
  min-height: 24px;
  color: #999;
  font-size: 18px;
}

.current-operation {
  color: white;
  font-size: 46px;
  word-break: break-all;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
}

button {
  height: 68px;
  border: none;
  border-radius: 18px;
  font-size: 22px;
  cursor: pointer;
  background: #333;
  color: white;
  transition: transform 0.1s ease, background 0.2s ease;
}

button:hover {
  background: #444;
}

button:active {
  transform: scale(0.96);
}

.function {
  background: #a5a5a5;
  color: #111;
}

.operator,
.equals {
  background: #ff9500;
}

.zero {
  grid-column: span 2;
}

@media (max-width: 400px) {
  .calculator {
    width: calc(100% - 30px);
  }
}