Tools for valid email template generation?

Question

Layout of letters

Are there libraries for creating a valid email template?
The bottom line is that the layout designer makes an email template based on the layout, and the library imports the styles and intersperses them into the html markup? The templates themselves are essentially simple, of course, without media queries, according to all the canons of the correctness of creating an html letter. It's just awkward to write markup in the html style attribute.

Answer 1

See https://mjml.io/

Answer 2

that is, you want someone to "on the fly" process your template, replacing classes with styles from some css ?
I think django-template-preprocessor will do