body {
  margin: 0;
  font-family: 'Segoe UI', sans-serif;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background: linear-gradient(135deg, #0f2027, #203a43, #2c5364);
  color: #fff;
}

.calculator {
  background: rgba(255, 255, 255, 0.1);
  padding: 20px;
  border-radius: 20px;
  box-shadow: 0 8px 25px rgba(0,0,0,0.3);
  backdrop-filter: blur(10px);
}

.display {
  background: rgba(0,0,0,0.3);
  padding: 20px;
  font-size: 2em;
  text-align: right;
  border-radius: 10px;
  margin-bottom: 15px;
  min-width: 260px;
  word-wrap: break-word;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 60px);
  gap: 10px;
  justify-content: center;
}

.btn {
  padding: 20px;
  border: none;
  border-radius: 10px;
  font-size: 1.2em;
  background: rgba(255,255,255,0.2);
  color: #fff;
  cursor: pointer;
  transition: transform 0.2s, background 0.2s;
}

.btn:hover {
  background: rgba(255,255,255,0.4);
  transform: scale(1.1);
}

.op {
  background: #f39c12;
}

.op:hover {
  background: #e67e22;
}

.ac {
  background: #e74c3c;
}

.ac:hover {
  background: #c0392b;
}

.equal {
  grid-column: 4 / 5;
  grid-row: 3 / 5;
  background: #2ecc71;
}

.equal:hover {
  background: #27ae60;
}

.zero {
  grid-column: span 2;
}

footer {
  margin-top: 20px;
  font-size: 0.9em;
  color: #ccc;
}