index.html

<!DOCTYPE html>
<html lang="pt-br">
    <head>
        <meta charset="UTF-8"/>
        <meta name="viewport" content="width=device-width, initial-scale=1.0"/>
        <meta http-equiv="X-UA-Compatible" content="ie=edge"/>
        <link rel="icon" href="img/favicon_000.png">
        <link rel="stylesheet" type="text/css" href="css/styles.css">
        <title>GitHub</title>
    </head>

    <body>
        <header id="main-header">
            <img src="img/favicon_fff.png" />
            <form>
                <input id="txt_user" type="text" placeholder="Username" />
                <input id="btn_find" type="submit" value="Find" />
            </form>
        </header>

        <div id="container"></div>

        <footer id="main-footer">
            <a href="./documentation.html">Documentation</a>
        </footer>

        <script src="js/index.js"></script>
        <script>
            const stopSubmitAction = event => {
                event.preventDefault();
            }
                
            document.getElementById('btn_find').addEventListener('click', stopSubmitAction);
        </script>
    </body>
</html>