* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
}

body {
  height: 100vh;
  background: linear-gradient(135deg, #667eea, #764ba2);
  display: flex;
  align-items: center;
  justify-content: center;
}

.calculator {
  background-color: #1e1e2f;
  padding: 20px;
  border-radius: 20px;
  box-shadow: 0 0 20px rgba(0, 0, 0, 0.5);
  width: 320px;
}

#display {
  width: 100%;
  height: 60px;
  font-size: 28px;
  text-align: right;
  padding: 10px;
  margin-bottom: 20px;
  border: none;
  border-radius: 10px;
  background-color: #2d2d44;
  color: #fff;
}

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

.btn {
  padding: 20px;
  font-size: 22px;
  border: none;
  border-radius: 10px;
  background-color: #3d3d5c;
  color: #fff;
  cursor: pointer;
  transition: 0.2s;
}

.btn:hover {
  background-color: #57577d;
}

.operator {
  background-color: #ff8c00;
  color: #fff;
}

.operator:hover {
  background-color: #e67e00;
}

.equal {
  grid-column: span 2;
  background-color: #06d6a0;
  color: #fff;
}

.equal:hover {
  background-color: #05c191;
}

.clear {
  background-color: #ef476f;
  color: #fff;
}

.clear:hover {
  background-color: #d63d61;
}

#backspace {
  background-color: #8d99ae;
  color: white;
}

#backspace:hover {
  background-color: #7a879b;
}