you shouldn't be editing those files directly,
you should be editing the Universal Email behavior to make changes to the email body.
if editing those files directly, the errors shouldn't make a big difference.
Bear in mind that the email does not use linked css, it uses In line CSS to set the design of the email. Email clients do not support linked CSS, this is why inline css is used.
See the "Customizing eCart email receipts" tutorial on the eCart support page: