[css-contain-2] Update Changelog

Author: frivoal

css-contain-2/Overview.bs

@@ -1928,6 +1928,14 @@ Changes from <a href="https://www.w3.org/TR/2020/WD-css-contain-2-20201216/">202
 </h3>
 
 * Included [=style containment=] in the ''strict'' and ''content'' keywords.
+* Use the [=overflow clip edge=] rather than the [=border edge=] when deciding if the element is “on screen”, as part of determining if it is [=relevant to the user=]
+* Define how animations and transitions act on skipped elements
+* Remove "at risk" marker from style containment
+* Disable propagation from the HTML body element when containment is on
+* Made style containment part of ''strict'' and ''content''
+* Clarify that scrollIntoView() doesn't scroll to children of a ''content-visibility:hidden'' element
+* Defined that elements having an ancestor with ''content-visibility: hidden'' don't generate boxes in the top layer
+* Defined that being in the top-layer makes an element relevant to the user
 
 <h3 id="changes-since-2020-06-03">
 Changes from <a href="https://www.w3.org/TR/2020/WD-css-contain-2-20200603/">2020-06-03 Working Draft</a>