[ui] Affix the page header to the top of the page

[philrenaud]

A report shows a 3rd party browser extension puts a banner at the top of page and awkwardly shifts nav; this fixes that

[github-actions]

Ember Test Audit comparison

	main	6b0cfc7	change
passes	1494	1494	0
failures	1	1	0
flaky	0	0	0
duration	000ms	000ms	-000ms

[philrenaud]

A little context for this: this is a position: fixed element, which means that you can scroll your browser generally, and wherever this element is when it started, it'll remain there. Perfect for headers, footers, etc.

A position: <anything but static> element's top, bottom, right or left properties will affect how near it is to some container. for position: absolute, this is the distance from the closest parent element with relative positioning. For position: fixed like this one, this is the distance from the browser's border.

As such, top: 0 indicates that it should always start at the very upper edge of the browser. Which it was doing already, unless some extension slots in before it to bump it down a few pixels. This just says "Even if that happens, start at y=0"

[tgross]

LGTM!