How to override the Craft forgot password email Struggling to find any documentation on how to override Craft's HTML for the forgotten password email.
The documentation can be found here:
https://craftcms.com/docs/templating/forgot-password-form

Part of the full templating documentation that starts here:
https://craftcms.com/docs/templating/global-variables

The actual HTML side of things is determined by the template you're using, which you can specify in the control panel -> settings -> emails.  I believe these settings are considered 'self documenting' in that there are explanations on that page as to what they do.

One thing worth noting is that IIRC you can't extend a layout template with that template, which is a little unfortunate.  So I have one general layout for all my general emails and duplicate that fully into the system email template.