In addition to automatically disabling the admin bar when there is excessive CSS (#1800), there should be an additional message displayed to the logged-in site administrator on the frontend when there is still excessive CSS. At the moment the ways for a user to know that there is excessive CSS are:

• Notice broken styling.
• See an AMP validation error when saving a post.
• Look at the page source for the amp-custom style manifest to see the excessive CSS message.

In addition to these, the plugin could display a message about the excessive CSS along with some suggestions for how to fix. For developers, fixing may involve rewriting CSS. For implementors, fixing may involving switching to a different theme or using alternative plugins. For other users, the fix may be to switch back to Classic/Legacy mode until the ecosystem better supports AMP.

The admin bar would be a good location to show this message: