I suspect that the fields are generated by html2pdf and not from html / css. Have you tried setting the fields in html2pdf-constructor ?
For instance. with array(0, 0, 0, 0) as the last parameter:
$html2pdf = new HTML2PDF('P', 'A4', 'en', true, 'UTF-8', array(0, 0, 0, 0));
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