* {
      box-sizing: border-box;
    }
    body {
      font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
      margin: 0;
      padding: 20px;
      background: #f0f4f8;
      color: #333;
    }
    h1 {
      text-align: center;
      margin-bottom: 30px;
    }
    .container {
      display: flex;
      justify-content: center;
      gap: 40px;
      max-width: 900px;
      margin: 0 auto;
      background: white;
      padding: 30px;
      border-radius: 12px;
      box-shadow: 0 8px 24px rgba(0,0,0,0.1);
      flex-wrap: wrap;
    }
    .form-container, .result-container {
      flex: 1 1 300px;
      min-width: 280px;
    }
    input[type="text"] {
      width: 100%;
      padding: 12px 15px;
      margin: 12px 0;
      border: 2px solid #ddd;
      border-radius: 8px;
      font-size: 16px;
      transition: border-color 0.3s ease;
    }
    input[type="text"]:focus {
      outline: none;
      border-color: #007bff;
      box-shadow: 0 0 8px rgba(0,123,255,0.3);
    }
    button {
      width: 100%;
      background-color: #007bff;
      color: white;
      border: none;
      padding: 14px;
      font-size: 18px;
      font-weight: bold;
      border-radius: 10px;
      cursor: pointer;
      margin-top: 15px;
      transition: background-color 0.3s ease;
    }
    button:hover {
      background-color: #0056b3;
    }

    /* Result styles */
    .result-container {
      padding: 20px;
      border-radius: 12px;
      min-height: 220px;
      background-color: #f9fafb;
      box-shadow: 0 4px 12px rgba(0,0,0,0.05);
      display: flex;
      flex-direction: column;
      justify-content: center;
      align-items: center;
      text-align: center;
      font-weight: 600;
      font-size: 18px;
      color: #333;
    }
    .result-text {
      margin: 10px 0;
    }
    .grade-A {
      background-color: #d4edda;
      color: #155724;
      border: 2px solid #c3e6cb;
      padding: 12px 20px;
      border-radius: 10px;
      font-weight: 700;
      font-size: 20px;
      width: 100%;
      max-width: 300px;
      margin: 10px 0;
    }
    .grade-B {
      background-color: #d1ecf1;
      color: #0c5460;
      border: 2px solid #bee5eb;
      padding: 12px 20px;
      border-radius: 10px;
      font-weight: 700;
      font-size: 20px;
      width: 100%;
      max-width: 300px;
      margin: 10px 0;
    }
    .grade-C {
      background-color: #fff3cd;
      color: #856404;
      border: 2px solid #ffeeba;
      padding: 12px 20px;
      border-radius: 10px;
      font-weight: 700;
      font-size: 20px;
      width: 100%;
      max-width: 300px;
      margin: 10px 0;
    }
    .grade-D {
      background-color: #ffe5b4;
      color: #664d03;
      border: 2px solid #ffdb58;
      padding: 12px 20px;
      border-radius: 10px;
      font-weight: 700;
      font-size: 20px;
      width: 100%;
      max-width: 300px;
      margin: 10px 0;
    }
    .grade-fail {
      background-color: #f8d7da;
      color: #721c24;
      border: 2px solid #f5c6cb;
      padding: 12px 20px;
      border-radius: 10px;
      font-weight: 700;
      font-size: 20px;
      width: 100%;
      max-width: 300px;
      margin: 10px 0;
    }
    #error {
      color: #d93025;
      font-weight: 700;
      font-size: 16px;
      margin-top: 15px;
    }

    @media (max-width: 700px) {
      .container {
        flex-direction: column;
        padding: 15px;
      }
      .form-container, .result-container {
        flex: 1 1 100%;
        min-width: 100%;
      }
      input[type="text"], button {
        font-size: 16px;
      }
      .result-container {
        min-height: auto;
        padding: 15px;
      }
      .result-container h1.text {
        font-size: 24px;
        margin-bottom: 20px;
      }
      .result-container h2.result-text {
        margin: 8px 0;
      }
    }