/* General styling */
body {
    font-family: 'Montserrat', sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    background-color: #1a1a1d;
  }
  
  /* Calculator container */
  #calculator {
    background-color: #2d2d30;
    border-radius: 20px;
    padding: 20px;
    box-shadow: 0 10px 20px rgba(0, 0, 0, 0.5);
    width: 350px;
    border: 1px solid #b8860b;
  }
  
  /* Display styling */
  #display {
    width: 90%;
    height: 60px;
    border: none;
    border-radius: 10px;
    text-align: right;
    padding: 15px;
    font-size: 2rem;
    background-color: #000;
    color: #f9f9f9;
    margin-bottom: 15px;
    box-shadow: inset 0 4px 8px rgba(0, 0, 0, 0.3);
    border: 1px solid #b8860b;
  }
  
  /* Calculator buttons */
  #keys {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
  }
  
  button {
    padding: 20px;
    border-radius: 10px;
    border: none;
    font-size: 1.5rem;
    cursor: pointer;
    transition: background-color 0.2s ease, transform 0.2s ease;
    color: #fff;
    background-color: #333;
    box-shadow: 0 4px 10px rgba(0, 0, 0, 0.3);
  }
  
  button:hover {
    background-color: #444;
    transform: translateY(-2px);
  }
  
  button:active {
    background-color: #555;
    transform: translateY(0);
  }
  
  /* Operators */
  .operator-btn {
    background-color: #b8860b;
    color: #fff;
  }
  
  .operator-btn:hover {
    background-color: #d4af37;
  }
  
  .operator-btn:active {
    background-color: #a67c00;
  }
  
  /* Equal button */
  button:nth-child(15) {
    background-color: #007f5f;
    color: #fff;
  }
  
  button:nth-child(15):hover {
    background-color: #009975;
  }
  
  button:nth-child(15):active {
    background-color: #005f43;
  }
  
  /* Clear button */
  button:nth-child(16) {
    background-color: #b8860b;
  }
  
  button:nth-child(16):hover {
    background-color: #d4af37;
  }
  
  button:nth-child(16):active {
    background-color: #a67c00;
  }