There is a new favourite app for Marketing Cloud users. CloudKettle where amongst other Eliot Harper (salesforce marketing cloud MVP) works, just released the content block MJML Live Editor. 

https://appexchange.salesforce.com/appxListingDetail?listingId=a0N3u00000Qt1wTEAR 

If your unfamiliar with MJML you can read more about it here https://mjml.io

In short it is a responsive email template framework that lets you focus on creating awesome content and not fiddle with making it fit all devices and email clients reaching your email.

Now you can skip the step of converting your MJML code to html.

This also may solve the preview issue in cloud pages that use external stylesheets. 

You would then be able to put your HTML code and inside MJML tags like this:

This may look something like this:

The content block is free so have a look at it :)