Inline CSS on Ghost Newsletter Themes. Necessary?

I’m build a newsletter theme.

I’m using TailwindCSS to style the newsletter theme.

Does Ghost auto-generate a newsletter optimized theme?

Is it necessary inline the CSS in the newsletter theme?

I have a Gulp plugin that can do this.

But, I’ve not read anywhere in the docs that this is necessary. The docs allude to Ghost auto-creating the email optimized theme itself. So, I’m guessing that means the Ghost either inlines the CSS or dumps the CSS libs in the HTML head?

Where can I test the newsletter optimized theme?
There is a screenshot in the docs of some kind of interface that displays the newsletter in a mobile browser and in desktop. Where is this preview? I’d like to check the output of the newsletter optimized theme (with all the CSS inlined for example). I know I can send a test email and check the output there. But is there a way to view the optimized version (if that is how it works) before sending an email?

Can I used Gulp to inline CSS for newsletter mode, and keep the CSS linked (not inlined) for desktop browser?
I can use something like https://maizzle.com/ to inline the Tailwind CSS, which would be good for users in email clients. But that isn’t very good for users in Chrome. I’d prefer to link the CSS in Desktop browsers, and not inline it.

Is it possible to pre-generate an email newsletter version of the theme, and have email readers use that? And have users visiting my website to see the “web version”

The newsletter html/css is not customisable. It’s a fixed template that has been highly optimised and tested across all major email clients.

I know I can send a test email and check the output there.

That’s the optimised output and includes all of the inlined styles.

The newsletter html/css is not customisable.
Are you sure about that?

This is a screen shot from the page https://ghost.org/newsletter-authors/

I’m seeing custom themes out there like…

Is this not a custom theme?

It is a custom theme, themes customise your public website, they do not customise the html/css used in the newsletter template.

Is there anyway to preview the email before sending it?