* {
  box-sizing: border-box;
  font-family: Segoe UI, sans-serif;
}

body {
  margin: 0;
  height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background: #ff9193;
}

.calculator {
  background: #f8f8f8;
  border-radius: 20px;
  box-shadow: 0 8px 25px rgba(0, 0, 0, 0.2);
  padding: 1rem;
  display: flex;
  flex-direction: column;
  gap: 1rem;
  width: 90%;
  max-width: 320px;
}

.display {
  background: #5ee6e6;
  border-radius: 20px;
  padding: 1rem;
  font-size: 2rem;
  text-align: right;
  color: #333;
  box-shadow: 0 2px 5px rgba(0, 0, 0, 0.1);
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0.7rem;
}

button {
  background: #f2f3f7;
  border: none;
  border-radius: 50%;
  padding: 1rem;
  font-size: 1.1rem;
  font-weight: bold;
  color: #333;
  box-shadow: 4px 4px 10px #ccc, -4px -4px 10px #fff;
  transition: all 0.2s, transform 0.1s;
  cursor: pointer;
}

button:hover {
  background-color: #e0e0e0;
  transform: scale(1.05);
}

button:active {
  box-shadow: 2px 2px 6px #bbb, inset -2px -2px 6px #fff;
  transform: scale(0.95);
}

.equal {
  grid-column: span 2;
  border-radius: 30px;
  background: #d78abc;
  color: white;
}

@media (max-width: 400px) {
  button {
    font-size: 1rem;
    padding: 0.8rem;
  }
}