[css-align-3] Change safe fallback to flex-start, so a scrolalble reversed flexbox actually fails safely. #11937

Author: tabatkins

css-align-3/Overview.bs

@@ -863,7 +863,7 @@ Overflow Alignment: the ''safe'' and ''unsafe'' keywords and scroll safety limit
 		<dt><dfn>safe</dfn>
 		<dd>
 			If the size of the <a>alignment subject</a> overflows the <a>alignment container</a>,
-			the <a>alignment subject</a> is instead aligned as if the alignment mode were ''start''.
+			the <a>alignment subject</a> is instead aligned as if the alignment mode were ''flex-start''.
 
 		<dt><dfn>unsafe</dfn>
 		<dd>
@@ -2539,6 +2539,9 @@ Changes</h2>
 		(<a href="https://github.com/w3c/csswg-drafts/issues/12106">Issue 12106</a>)
 	* Allow safe/unsafe to be specified with ''justify-self/normal''.
 		(<a href="https://github.com/w3c/csswg-drafts/issues/12920">Issue 12920</a>)
+	* Change safe alignment to cause the container to fall back to ''flex-start'',
+		so it is correctly safe for a scrollable reversed flexbox.
+		(<a href="https://github.com/w3c/csswg-drafts/issues/11937">Issue 11937</a>)
 
 	See also <a href="https://www.w3.org/TR/2025/WD-css-align-3-20250311/#changes">previous changes</a>.