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

body {
  font-family: 'Poppins', sans-serif;
  background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
}

.container {
  width: 100%;
  padding: 15px;
}

.calculator {
  max-width: 400px;
  margin: 0 auto;
  background: rgba(255, 255, 255, 0.95);
  border-radius: 20px;
  box-shadow: 0 20px 60px rgba(0, 0, 0, 0.3);
  padding: 30px 20px;
  backdrop-filter: blur(10px);
}

.calculator h2 {
  text-align: center;
  color: #333;
  margin-bottom: 25px;
  font-size: 24px;
  font-weight: 600;
}

.display {
  margin-bottom: 25px;
}

#result {
  width: 100%;
  height: 70px;
  font-size: 32px;
  text-align: right;
  padding: 10px 20px;
  border: 2px solid #e0e0e0;
  border-radius: 12px;
  outline: none;
  font-family: 'Poppins', sans-serif;
  font-weight: 500;
  background: #f8f9fa;
  color: #333;
  box-shadow: inset 0 2px 5px rgba(0, 0, 0, 0.1);
}

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

.btn {
  padding: 20px 5px;
  font-size: 20px;
  border: none;
  border-radius: 12px;
  cursor: pointer;
  font-weight: 500;
  transition: all 0.2s ease;
  font-family: 'Poppins', sans-serif;
  background: #f0f0f0;
  color: #333;
  box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
}

.btn:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 12px rgba(0, 0, 0, 0.15);
}

.btn:active {
  transform: translateY(0);
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

.number {
  background: #ffffff;
  color: #333;
}

.number:hover {
  background: #e8e8e8;
}

.operator {
  background: #ff9f43;
  color: white;
  font-weight: 600;
}

.operator:hover {
  background: #ff8c21;
}

.clear {
  background: #ff6b6b;
  color: white;
  font-weight: 600;
}

.clear:hover {
  background: #ff5252;
}

.delete {
  background: #95a5a6;
  color: white;
  font-weight: 600;
}

.delete:hover {
  background: #7f8c8d;
}

.equals {
  background: #10ac84;
  color: white;
  font-size: 28px;
  font-weight: 600;
  grid-row: span 2;
}

.equals:hover {
  background: #0e9c78;
}

.zero {
  grid-column: span 2;
}

/* Mobile Responsive */
@media (max-width: 480px) {
  .calculator {
    padding: 20px 15px;
  }

  .calculator h2 {
    font-size: 20px;
    margin-bottom: 20px;
  }

  #result {
    height: 60px;
    font-size: 28px;
  }

  .btn {
    padding: 15px 5px;
    font-size: 18px;
  }

  .equals {
    font-size: 24px;
  }
}

@media (max-width: 350px) {
  .btn {
    padding: 12px 5px;
    font-size: 16px;
  }

  .equals {
    font-size: 20px;
  }
}