* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
  }
  
  html, body {
    height: 100%;
    overflow: hidden; /* Prevents page scrolling */
  }
  
  body {
    display: flex;
    justify-content: center;
    align-items: center;
    font-family: Arial, sans-serif;
    background-color: #f5f5f5;
    padding: 20px;
  }
  
  .calculator {
    width: 100%;
    max-width: 400px; /* Slightly wider */
    background-color: #333;
    border-radius: 10px;
    overflow: hidden;
    box-shadow: 0px 4px 10px rgba(0, 0, 0, 0.1);
  }
  
  .display input {
    width: 100%;
    padding: 20px;
    font-size: 1.5em;
    color: #fff;
    background-color: #444;
    border: none;
    outline: none;
    text-align: right;
  }
  
  .buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
  }
  
  button {
    padding: 18px;
    font-size: 1.1em;
    color: #333;
    background-color: #ddd;
    border: 1px solid #333;
    outline: none;
    cursor: pointer;
    transition: background-color 0.3s ease;
  }
  
  button:hover {
    background-color: #bbb;
  }
  
  button:nth-child(4n) {
    background-color: #ff8c00;
    color: #fff;
  }
  
  button:nth-last-child(-n+10) {
    background-color: #4CAF50;
    color: #fff;
  }