Then as far as I can tell from my browser inspector a selector of tr.tr-invoice-details-desc strong should be enough to target that, or possibly tr.tr-invoice-details-desc .invoice-details-left-td strong if the former isn’t specific enough.
You could target the table cell in this way and use the content property to override. However this would only work with the web view and will be ignored on the PDF output (due to it’s more primitive interpretation of CSS).
To get around this we created a set of CSS transform classes that get parsed out on the server to override specific labels on the invoice.
We’ll have a look at this later today, but I suspect there’s no transform label for “Invoice Name”.