Summary

This override AMP's CSS:

html.i-amphtml-fie:not(.i-amphtml-inabox)>body,
html.i-amphtml-singledoc:not(.i-amphtml-inabox)>body {
    position: relative!important;
}

By forcing the position to be unset, thus allowing the Admin Bar's position:absolute to be positioned outside of the body. AMP's CSS here is only relevant in the AMP viewer context, in which an AMP page with the Admin Bar in Dev Mode will never appear.

FIxes #3436.

Checklist

• My pull request is addressing an open issue (please create one otherwise).
• My code is tested and passes existing tests.
• My code follows the Engineering Guidelines (updates are often made to the guidelines, check it out periodically).