body {
      font-family: 'Orbitron', sans-serif;
      background-color: #f5f6f7;
      color: #000;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100vh;
      padding: 20px;
      transition: all 0.3s ease-in-out;
    }
    .dark-mode body, body.dark-mode {
      background-color: #1e1e1e;
      color: #fff;
    }
    .calculator {
      background-color: #fff;
      padding: 25px;
      border-radius: 20px;
      box-shadow: 0 8px 24px rgba(0, 0, 0, 0.15);
      width: 320px;
      transition: all 0.3s;
    }
    .dark-mode .calculator, body.dark-mode .calculator {
      background-color: #2c2c2c;
    }
    .display {
      background: #f0f0f0;
      color: #000;
      font-size: 2rem;
      padding: 15px;
      border-radius: 12px;
      text-align: right;
      margin-bottom: 20px;
      min-height: 60px;
      overflow-x: auto;
      white-space: nowrap;
    }
    .dark-mode .display, body.dark-mode .display {
      background: #1c1c1c;
      color: #0f0;
    }
    .btn-custom {
      font-size: 1.3rem;
      padding: 15px;
      border-radius: 12px;
      transition: transform 0.2s;
    }
    .btn-custom:hover {
      transform: scale(1.05);
    }
    .btn-operator {
      background-color: #ffc107;
      color: #000;
    }
    .btn-equal {
      background-color: #28a745;
      color: #fff;
    }
    .btn-clear {
      background-color: #dc3545;
      color: #fff;
    }
    .btn-function {
      background-color: #0d6efd;
      color: #fff;
    }

    #themeToggle {
      position: fixed;
      top: 15px;
      right: 15px;
      z-index: 1000;
      border: 1px solid #ccc;
      background: #fff;
      padding: 8px 10px;
      border-radius: 8px;
      cursor: pointer;
    }
    .dark-mode #themeToggle, body.dark-mode #themeToggle {
      background: #333;
      color: #fff;
      border: 1px solid #666;
    }

    footer {
      margin-top: 60px;
      padding: 16px;
      width: 100%;
      background-color: #f8f9fa;
      border-top: 1px solid #dee2e6;
      text-align: center;
    }
    .dark-mode footer, body.dark-mode footer {
      background-color: #fff;
      color: #000;
    }
    footer a {
      text-decoration: none;
      font-weight: 600;
      color: #000;
    }
    .dark-mode footer a, body.dark-mode footer a {
      color: #000;
    }