WooCommerce uses the Emogrifier class to add inline styles to the email. It is a small utility to convert css to in-line styles.

However, while parsing your template, this breaks some of styles you have made.

That is the reason why a few of the styles got broke.

Solution is to change the styles for that block (You can re-design that block alone)

If it keeps breaking, then here is a quick workaround

Edit wp-content/plugins/woocommerce/includes/emails/class-wc-email.php

Around line 462, you will find

$content    = $emogrifier->emogrify();

Change this to

//$content    = $emogrifier->emogrify();

Save

This would mean that the content does not pass through emogrifier utility.

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