Hi - to change the width the code is in the line ~439
templates/your_template/html/com_virtuemart/productdetails/default.php
<a class="FlexibleAskforPrice" <?php if (!($parameter == "quicklook")) { ?>rel="facebox" rev="iframe|550|
650"<?php } ?>
re change the style - the whole popup is surrounded by a div with the class ask-a-question-view
so just target in your template css that e.g.
div.ask-a-question-view {
font-family: comic sans ms;
}