One Of Those "Onboarding" UIs, With Anchor Positioning | CSS-Tricks
Briefly

"Anchor positioning lets us attach - or 'anchor' - one element to one or more other elements, helping absolutely-positioned elements behave as expected."
"Currently, anchor positioning is a W3C draft spec with limited availability, specifically for Chromium-based browsers, but there’s a polyfill available for wider compatibility."
Read at CSS-Tricks
[
|
]