* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
  font-family: "SF Pro Display", sans-serif;
}

body {
  background: #e0e0e0;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
}

.frame {
  background: #f5f5f7;
  border-radius: 20px;
  width: 350px;
  padding: 20px;
  box-shadow: 0 10px 40px rgba(0, 0, 0, 0.2);
  position: relative;
}

.stand {
  width: 80px;
  height: 15px;
  background: #d0d0d0;
  border-radius: 0 0 10px 10px;
  margin: 20px auto 0;
}

.calculator {
  background: #1e1e1e;
  border-radius: 15px;
  padding: 20px;
  color: white;
  display: flex;
  flex-direction: column;
  gap: 10px;
}

#input {
  background: #000;
  height: 60px;
  text-align: right;
  padding: 10px;
  font-size: 2rem;
  border-radius: 10px;
  color: white;
  box-shadow: inset 0 0 10px #00ff8866;
}

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

button {
  height: 60px;
  border: none;
  border-radius: 12px;
  font-size: 1.2rem;
  background: #3a3a3a;
  color: white;
  cursor: pointer;
  transition: all 0.2s ease;
}

button:hover {
  background: #4a4a4a;
}

button:active {
  transform: scale(0.98);
}

button:nth-child(4n) {
  background: #ff9500;
}

button:nth-child(4n):hover {
  background: #ffa733;
}

.zero {
  grid-column: span 2;
}