body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  font-family: Arial, sans-serif;
  transition: background 0.3s;
}

body.dark {
  background: #1e1e2f;
}

body.dark .calculator {
  background: #2c2c3e;
}

body.dark button {
  background: #4b4b6a;
  color: #fff;
}

body.dark #display {
  background: #fff;
  color: #000;
}

body.light {
  background: #f2f2f2;
}

body.light .calculator {
  background: #ffffff;
}

body.light button {
  background: #e0e0e0;
  color: #000;
}

body.light #display {
  background: #f9f9f9;
  color: #000;
}

.calculator {
  padding: 20px;
  border-radius: 12px;
  width: 270px;
}

.top {
  display: flex;
  gap: 10px;
}

#display {
  flex: 1;
  height: 50px;
  font-size: 22px;
  text-align: right;
  padding: 10px;
  border: none;
  border-radius: 8px;
}

.mode-btn {
  width: 45px;
  border-radius: 8px;
  cursor: pointer;
}

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

button {
  height: 50px;
  font-size: 18px;
  border: none;
  border-radius: 8px;
  cursor: pointer;
}

button:hover {
  opacity: 0.85;
}

.equal {
  grid-row: span 2;
  background: #ff7a18 !important;
  color: #fff;
}

.zero {
  grid-column: span 2;
}