* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: Arial, Helvetica, sans-serif;
  background-color: #1e1e1e;
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  padding: 20px;
}

.calculator {
  width: 100%;
  max-width: 320px;
  background-color: #2b2b2b;
  border-radius: 12px;
  padding: 15px;
}

.screen {
  background-color: #111;
  color: white;
  border-radius: 10px;
  padding: 15px;
  margin-bottom: 15px;
  word-wrap: break-word;
  word-break: break-all;
}

.previous {
  min-height: 20px;
  font-size: 14px;
  color: #aaa;
  text-align: right;
}

.current {
  min-height: 40px;
  font-size: 32px;
  text-align: right;
  margin-top: 5px;
}

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

button {
  height: 60px;
  border: none;
  border-radius: 10px;
  font-size: 20px;
  cursor: pointer;
}

button:hover {
  opacity: 0.9;
}

.number {
  background-color: #444;
  color: white;
}

.gray {
  background-color: #666;
  color: white;
}

.orange {
  background-color: orange;
  color: black;
}

.blue {
  background-color: #4da6ff;
  color: white;
}

.zero {
  grid-column: span 2;
}

@media (max-width: 400px) {
  .calculator {
    max-width: 100%;
  }

  button {
    height: 55px;
    font-size: 18px;
  }

  .current {
    font-size: 28px;
  }
}