Integrating third party HTML for mailist list automation without CSS

So
I receive a block of HTLM script to support instant subscription to my newsletter direct into the mailing solution I signed up for. However the code comes without a CSS so it looks really ugly in my page I would like to reshape better position it to my home page.

    <form name='cadastro' action='https://ga.mediapost.com.br/ptit/ptit_processa.php' method='post'>
<input type='hidden' id='hash' name='hash' value='LNPK033159' /> <!-- Não alterar este campo -->
<input type='hidden' id='htm_response' name='htm_response' value='1' /> <!-- Este campo ajusta os caracteres especiais dos avisos -->
<input type='hidden' id='cod_lista' name='cod_lista' value='540' /> <!-- O valor deste campo é o códigoo da lista onde os contatos serão adicionados em sua conta -->
<label>E-mail</label> <input type='email' id='mp-email' name='mp-email' value='' placeholder='E-mail' required /><br/>
<input type='submit' name='submit' value='Enviar' />
</form>

I could not paste it into a proper container so a class could not be assigned to it. Any hit for me?