* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Arial', sans-serif;
  }
  
  body {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background: #1b1b1b;
    padding: 0 15px;
  }
  
  .calculator {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
    max-width: 320px;
    width: 100%;
  }
  
  .calculator .value {
    grid-column: span 4;
    height: 100px;
    text-align: right;
    border: none;
    outline: none;
    padding: 15px;
    font-size: 2rem;
    background: #292929;
    color: white;
    border-radius: 5px;
  }
  
  .calculator span {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 60px;
    background: #292929;
    border: 1px solid rgba(0, 0, 0, 0.1);
    color: #fff;
    font-size: 1.5rem;
    border-radius: 5px;
    cursor: pointer;
  }
  
  .calculator span:hover {
    background: #03b1ff;
  }
  
  .calculator span:active {
    background: #ff9f00;
    color: #fff;
  }
  
  .calculator span.clear {
    grid-column: span 2;
    background: #ff9f00;
    color: white;
  }
  
  .calculator span.plus {
    grid-row: span 2;
    height: 120px;
    background: #ffc107;
  }
  
  .calculator span.equal {
    background: #28a745;
    color: white;
  }
  
  .calculator .num, .calculator .num.plus, .calculator .equal, .calculator .clear {
    font-weight: bold;
  }
  
  @media (max-width: 380px) {
    .calculator {
      grid-template-columns: repeat(4, 1fr);
    }
    .calculator .value {
      font-size: 1.8rem;
      padding: 12px;
    }
    .calculator span {
      font-size: 1.3rem;
      height: 55px;
    }
  }