* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
}

body {
  min-height: 100vh;
  display: grid;
  place-items: center;
  background: #f3f4f6;
}

.calculator {
  width: 320px;
  padding: 20px;
  background: #ffffff;
  border-radius: 22px;
  border: 1px solid #e5e7eb;
  box-shadow: 0 25px 45px rgba(0, 0, 0, 0.08);
}

#display {
  width: 100%;
  height: 72px;
  margin-bottom: 18px;
  padding: 10px 14px;
  font-size: 2.2rem;
  text-align: right;
  border-radius: 14px;
  border: 1px solid #e5e7eb;
  background: #ffffff;
  color: #374151;
  outline: none;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 14px;
}

button {
  height: 58px;
  border-radius: 14px;
  border: 1px solid rgba(0, 0, 0, 0.05);
  font-size: 1.2rem;
  cursor: pointer;
  background: #f1f1f1;
  color: #111827;
  box-shadow: 0 6px 12px rgba(0, 0, 0, 0.06);
  transition: transform 0.12s ease, box-shadow 0.12s ease, background 0.2s ease;
}

button:hover {
  background: #e5e7eb;
}

button:active {
  transform: scale(0.95);
  box-shadow: 0 3px 6px rgba(0, 0, 0, 0.08);
}

.action {
  background: #d4d4d4;
  font-weight: 500;
}

.operator {
  background: #f3f4f6;
  color: #f97316;
  font-weight: 600;
}

.equal {
  background: #f97316;
  color: #ffffff;
  font-weight: 700;
}

.equal:hover {
  background: #ea580c;
}