Google Fonts

Google Fonts é uma bibliotecas com mais de mil fontes livres licenciadas.

Site: https://fonts.google.com/

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Arquivo: index.html
<!doctype html>
<html lang="pt-br">
<head>
       <meta charset="utf-8">
       <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Alterando a Fonte no HTML5</title>
</head>

<body>
<style>
@font-face {
    font-family: 'kelly'; src: url(html5/kelly.ttf);
}
#fonte {
    font-family: 'kelly'
}
</style>
<p id="fonte">Quis nostrud exercitation ullamco laboris nisi consectetur adipisicing elit. Ut aliquip ex ea commodo consequat. Duis aute irure dolor qui officia deserunt velit esse cillum dolore. Ullamco laboris nisi sed do eiusmod tempor incididunt consectetur adipisicing elit.</p>
</body>
</html>