@import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;600&display=swap');

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

body {
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  background: linear-gradient(135deg, #121212, #1f1f1f);
  font-family: 'Inter', sans-serif;
}

.calculator {
  width: 360px;
  background: rgba(30, 30, 30, 0.85);
  border-radius: 24px;
  box-shadow: 0 15px 40px rgba(0, 0, 0, 0.6);
  backdrop-filter: blur(30px);
  padding: 30px 25px;
  border: 1px solid rgba(255, 255, 255, 0.05);
  transition: all 0.3s ease;
}

#display {
  width: 100%;
  height: 70px;
  font-size: 32px;
  font-weight: 600;
  text-align: right;
  padding: 20px;
  margin-bottom: 25px;
  border: none;
  border-radius: 12px;
  background: rgba(255, 255, 255, 0.05);
  color: #f1f1f1;
  outline: none;
  box-shadow: inset 0 0 10px rgba(0, 0, 0, 0.25);
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 15px;
}

.btn {
  padding: 22px;
  font-size: 20px;
  border: none;
  border-radius: 14px;
  background: rgba(255, 255, 255, 0.06);
  color: #ffffff;
  font-weight: 500;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.2);
  cursor: pointer;
  transition: all 0.2s ease-in-out;
  backdrop-filter: blur(8px);
  position: relative;
  overflow: hidden;
}

.btn:hover {
  background: rgba(255, 255, 255, 0.12);
  transform: translateY(-2px);
  box-shadow: 0 6px 18px rgba(0, 0, 0, 0.3);
}

.btn:active {
  transform: scale(0.96);
  background: rgba(255, 255, 255, 0.2);
}

/* Special buttons */
.operator {
  background: rgba(0, 150, 255, 0.15);
  color: #64b5f6;
}

.operator:hover {
  background: rgba(0, 150, 255, 0.25);
  color: #90caf9;
}

.function {
  background: rgba(255, 193, 7, 0.15);
  color: #ffca28;
}

.function:hover {
  background: rgba(255, 193, 7, 0.25);
}

.equal {
  grid-row: span 2;
  background: #00e676;
  color: #000;
  font-weight: bold;
  font-size: 24px;
  box-shadow: 0 4px 15px rgba(0, 230, 118, 0.5);
}

.equal:hover {
  background: #00c853;
  box-shadow: 0 6px 20px rgba(0, 200, 83, 0.6);
}

.zero {
  grid-column: span 2;
}