.heading
{
    text-align: center;
}

.calculator {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    grid-gap: 8px;
    max-width: 300px;
    margin: 0 auto;
    padding: 16px;
    background-color: #f5f5f5;
    border-radius: 8px;
  }
  
  .value {
    grid-column: span 4;
    padding: 8px;
    font-size: 1.5em;
    text-align: right;
    border: 1px solid #ccc;
    border-radius: 4px;
  }
  
  .num-clear {
    grid-column: span 2;
    background-color: #f44336;
    color: #fff;
    padding: 8px;
    text-align: center;
    cursor: pointer;
    border-radius: 4px;
  }
  
  span {
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 12px;
    font-size: 1.2em;
    background-color: #e0e0e0;
    border: 1px solid #ccc;
    border-radius: 4px;
    cursor: pointer;
  }
  
  span:hover {
    background-color: #ccc;
  }