index.html

<!DOCTYPE html>
<html lang="pt-BR">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <link rel="icon" href="imagens/lua.png">
    <link rel="stylesheet" href="css/styles.css" />
    <title>Decifre</title>
<audio controls>
	<source src="music/AERØHEAD - HAVEN  No Copyright Music.mp3">
</audio>
  </head>
  <body>
    
    <style>
      @font-face{
        font-family: 'Maneira';
        src: url('Fipps-Regular.otf');
        font-weight: normal;
        font-style: normal;
      }
      @import url('https://fonts.googleapis.com/css2?family=Bungee+Spice&display=swap');
      </style>
  <div class="box">
    <form class="forms" name="formulario">

      <fieldset>
        <legend>Decifre seu código!</legend>
  
        <div class="entrada">
          <input type="text" name="texto" id="texto" class="inputTexto" placeholder="Digite sua mensagem"/>
        </div>

        <div class="modo">
          <div class="a"><label for="option">Escolha o modo</label></div>
          <select name="chooseCod" class="chooseCod" id="escolherCod" required>
            <option value="semValor" id="semValor" disabled selected>---</option>
            <option value="cCesar" id="cCesar">Cifra de César</option>
            <option value="Base64" id="base64">Base64</option>
          </select>
        </div>

        <div class="incremento" style="display: none" id="valorIncremento">
          <p>Incremento da chave</p>
          <input type="number" class="inputIncremento" id="numeroIncrementos" default="0" min="1" value="1" />
        </div>

        <div class="codif">
          <input type="radio" name="codific" id="codificar" class="radioBtn" value="codificar" /><label for="codificar">Codificar</label>
          <input type="radio" name="codific" id="decodificar"  class="radioBtn" value="decodificar" /><label for="decodificar">Decodificar</label>
        </div>

        <div class="areabtn">
          <button type="submit" class="btn" name="codMsg" id="submit">Codificar mensagem</button>
        </div>

        <div class="saida">
          <textarea disabled class="areaSaida" id="saidaTexto" placeholder="Sua descoberta!"></textarea>
        </div>
      </fieldset>
    </form>
  </div>
    <script src="script.js"></script>
  </body>
</html>