:root {
  --bg: linear-gradient(135deg, #667eea, #764ba2);
  --card: white;
  --text: black;
}

body.dark {
  --bg: #111;
  --card: #1e1e1e;
  --text: white;
}

body {
  margin: 0;
  height: 100vh;
  background: var(--bg);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  font-family: Arial, sans-serif;
}

.top {
  display: flex;
  justify-content: space-between;
  width: 260px;
  margin-bottom: 10px;
  color: white;
}

.calculator {
  background: var(--card);
  color: var(--text);
  padding: 15px;
  border-radius: 12px;
  width: 260px;
  box-shadow: 0 5px 20px rgba(0,0,0,0.3);
}

#display {
  width: 100%;
  height: 50px;
  margin-bottom: 10px;
  font-size: 20px;
  text-align: right;
  padding: 10px;
  box-sizing: border-box;
}

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

button {
  padding: 15px;
  font-size: 16px;
  cursor: pointer;
}

.zero {
  grid-column: span 2;
}