[Desafio] Mão na Massa | HTML e CSS: ambientes de desenvolvimento, estrutura de arquivos e tags

<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8" />
    <meta name="description" content="Free Web tutorials" />
    <meta name="keywords" content="HTML,CSS,XML,JavaScript" />
    <meta name="author" content="Fernanda Ferreira" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <style>
      body {
        margin: 0;
        font-family: Arial, Helvetica, sans-serif;
      }

      .topnav {
        width: 100%;
        overflow: hidden;
        background-color: #333;
      }

      .topnav a {
        display: flex;
        float: left;
        color: #f2f2f2;
        text-align: center;
        padding: 14px 16px;
        text-decoration: none;
        font-size: 17px;
        width: 22%;
      }

      .topnav a:hover {
        background-color: #ddd;
        color: black;
      }

      .topnav a.active {
        background-color: #aa6d04;
        color: white;
      }

      .topnav div {
        background-color: #aa6d04;
        color: white;
      }

      img {
        border: 1px solid #ddd;
        border-radius: 4px;
        padding: 5px;
        width: 600px;
      }

      img:hover {
        box-shadow: 0 0 2px 1px rgba(0, 140, 186, 0.5);
      }

      .center {
        display: flex;
        width: 100%;
        flex-wrap: wrap;
        align-content: center;
        flex-direction: column;
        padding-top: 75px;
      }
      .fixarRodape {
        bottom: 0;
        position: fixed;
        width: 100%;
        text-align: center;
      }

      .fixarCabeçalho {
        top: 0;
        position: fixed;
        width: 100%;
        text-align: center;
      }
    </style>
  </head>
  <body>
    <header class="fixarCabeçalho">
      <div class="topnav">
        <a class="active" href="#home">Home</a>
        <a href="#news">Notícias</a>
        <a href="#contact">Contato</a>
        <a href="#about">Sobre</a>
      </div>
    </header>

    <main>
      <div class="center">
        <div>
          <h1>Mão na massa 2</h1>
          <p>Praticando...</p>
        </div>
        <div>
          <a target="_blank" href="download.png">
            <img src="download.png" alt="Gatinho" />
          </a>
        </div>
      </div>
    </main>
    <footer class="fixarRodape">
      <div class="topnav">
        <div>
          <p>
            Desenvolvedora: Fernanda Ferreira<br />
            <a href="fernanda@example.com">fernanda@example.com</a>
          </p>
        </div>
      </div>
    </footer>
  </body>
</html>