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

body {
  background: linear-gradient(135deg, #1e293b, #0f172a);
  color: white;
  font-family: Arial, sans-serif;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
}

.calculator {
  background: #1e293b;
  border-radius: 20px;
  box-shadow: 0 10px 30px rgba(0,0,0,0.5);
  overflow: hidden;
  width: 320px;
}

.display {
  background: #0f172a;
  padding: 15px;
}

.display input {
  width: 100%;
  height: 60px;
  background: none;
  border: none;
  color: white;
  font-size: 2rem;
  text-align: right;
  outline: none;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
  padding: 15px;
}

.btn {
  background: #334155;
  border: none;
  padding: 20px;
  font-size: 1.2rem;
  border-radius: 10px;
  color: white;
  cursor: pointer;
  transition: background 0.2s ease;
}

.btn:hover {
  background: #475569;
}

.operator {
  background: #f59e0b;
  color: black;
}

.operator:hover {
  background: #d97706;
}

.equals {
  background: #10b981;
  color: black;
  grid-column: span 1;
}

.equals:hover {
  background: #059669;
}

.zero {
  grid-column: span 2;
}