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

body {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background: linear-gradient(135deg, #1d2b64, #f8cdda);
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

.calculator {
  width: min(340px, 95vw);
  background: #f7f7f7;
  border-radius: 20px;
  padding: 20px;
  box-shadow: 0 20px 45px rgba(0,0,0,0.2);
}

.calculator h1 {
  text-align: center;
  margin-bottom: 16px;
  color: #2f2f2f;
}

.display input {
  width: 100%;
  font-size: 2rem;
  text-align: right;
  border: 2px solid #ddd;
  border-radius: 12px;
  padding: 14px 16px;
  background: #fff;
  color: #111;
}

.buttons {
  margin-top: 16px;
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
}

button {
  border: none;
  border-radius: 12px;
  padding: 18px;
  font-size: 1.25rem;
  background: #e3e3e3;
  transition: transform .1s ease, background .15s ease;
  cursor: pointer;
}

button:hover {
  transform: translateY(-1px);
}

button:active {
  transform: translateY(1px);
}

button[data-action="equals"] {
  background: #03a87c;
  color: #fff;
}

button[data-action="clear"], button[data-action="backspace"] {
  background: #f25c54;
  color: #fff;
}

button.wide {
  grid-column: span 2;
}