As far as the PDF goes, Custom Themes are your fix.
However, if you are talking about the email bodies, I’m not sure what the current status of email templates.
We used to have fully working Email Templates using Liquid code, but that is being slowly phased out and no fully functioning alternative is presented for dynamic content. So my advise is this:
You can use html & css inside your Email Templates to make your emails a bit more fancy.
For dynamic content, my advise is to wait until a fully functioning alternative is provided. This is what I have done as I removed all dynamic content from my email bodies for now and made my emails generic.