see <https://ews-build.s3-us-west-2.amazonaws.com/Windows-EWS/r443758-113158/fast/forms/auto-fill-button/input-auto-filled-credit-card-diffs.html> (note that the file/bug used to be named something else, but was changed to better clarify the feature) note how not even the background is the right color o_0 nothing in `html.css` seems to suggest that this wouldn't work
For what it's worth it doesn't seem to work on GTK either (with the same issue that the background isn't the right color): https://build.webkit.org/results/GTK-Linux-64-bit-Release-Tests/r285738%20(4706)/fast/forms/auto-fill-button/input-auto-filled-and-obscured-diffs.html
<rdar://problem/85520654>