* {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }

    body {
      font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
      background-color: #f0f4f8;
      color: #222;
      padding: 0;
      margin: 0;
    }

    header {
      background-color: #1e88e5;
      color: white;
      padding: 20px;
      text-align: center;
      box-shadow: 0 2px 6px rgba(0,0,0,0.1);
    }

    header h1 {
      font-size: 26px;
    }

    nav a {
      color: #fff;
      text-decoration: underline;
      font-weight: 500;
      display: inline-block;
      margin-top: 10px;
    }

    main {
      padding: 30px 20px;
      text-align: center;
      display: flex;
      justify-content: center;
      align-items: center;
      flex-direction: column;
      height: 70vh;
    }

    main p {
      font-size: 18px;
      margin-bottom: 20px;
    }

    form {
      background-color: #fff;
      padding: 25px;
      max-width: 450px;
      margin: 0 auto;
      border-radius: 12px;
      box-shadow: 0 0 15px rgba(0, 0, 0, 0.05);
    }

    input[type="number"] {
      width: 100%;
      padding: 14px;
      font-size: 16px;
      border-radius: 8px;
      border: 1px solid #ccc;
      margin-bottom: 15px;
    }

    button {
      width: 100%;
      padding: 14px;
      font-size: 16px;
      background-color: #1e88e5;
      color: white;
      border: none;
      border-radius: 8px;
      cursor: pointer;
      transition: 0.3s;
    }

    button:hover {
      background-color: #1565c0;
    }

    .result {
      margin-top: 20px;
      font-size: 18px;
      font-weight: bold;
      color: #ff0000;
    }

    footer {
      margin-top: 50px;
      background-color: #1e88e5;
      color: white;
      text-align: center;
      padding: 15px;
      font-size: 14px;
    }

    @media (max-width: 500px) {
      header h1 {
        font-size: 22px;
      }

      main p {
        font-size: 16px;
      }
    }