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

body {
  font-family: 'Segoe UI', sans-serif;
  background: linear-gradient(135deg, #667eea, #764ba2);
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
}

.calculator {
  background: #1e1e2f;
  padding: 20px;
  border-radius: 20px;
  box-shadow: 0 15px 35px rgba(0, 0, 0, 0.4);
  width: 320px;
}

.display {
  background: #0f0f1a;
  color: white;
  font-size: 2.5rem;
  text-align: right;
  padding: 20px;
  border-radius: 12px;
  margin-bottom: 15px;
  min-height: 80px;
  overflow: hidden;
  box-shadow: inset 0 4px 10px rgba(0, 0, 0, 0.5);
}

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

.btn {
  height: 65px;
  font-size: 1.4rem;
  border: none;
  border-radius: 12px;
  cursor: pointer;
  transition: all 0.2s;
}

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

.btn.operator {
  background: #ff9500;
  color: white;
  font-weight: bold;
}

.btn.clear, .btn.delete {
  background: #a6a6a6;
  color: black;
  font-weight: bold;
}

.btn.equals {
  background: #00d26a;
  color: white;
  font-size: 1.6rem;
  grid-row: span 2;
}

.zero {
  grid-column: span 2;
}

.btn:hover {
  opacity: 0.9;
}