* { box-sizing: border-box; }
    body {
      font-family: Arial, sans-serif;
      background: #1e293b;
      display: flex;
      justify-content: center;
      align-items: center;
      height: 100vh;
      margin: 0;
    }
    .calculator {
      background: #0f172a;
      padding: 15px;
      border-radius: 10px;
      box-shadow: 0 5px 20px rgba(0,0,0,0.5);
    }
    .display {
      background: #1e293b;
      color: white;
      font-size: 2rem;
      text-align: right;
      padding: 10px;
      border-radius: 5px;
      margin-bottom: 10px;
      overflow-x: auto;
    }
    .buttons {
      display: grid;
      grid-template-columns: repeat(4, 60px);
      gap: 10px;
    }
    button {
      padding: 15px;
      font-size: 1.2rem;
      border: none;
      border-radius: 5px;
      cursor: pointer;
      background: #334155;
      color: white;
      transition: background 0.2s;
    }
    button:hover {
      background: #475569;
    }
    .operator {
      background: #2563eb;
    }
    .operator:hover {
      background: #1d4ed8;
    }
    .equal {
      grid-column: span 2;
      background: #16a34a;
    }
    .equal:hover {
      background: #15803d;
    }
    .clear {
      background: #dc2626;
    }
    .clear:hover {
      background: #b91c1c;
    }