[css-ui-4] update usage of "all: default" to "all: revert"

Author: frivoal

css-ui-4/Overview.bs

@@ -718,7 +718,7 @@ they intended, possibly by using ''all: unset''.
 Issue: This usage of the 'all' property would remove focus indicators
 created by the 'outline' property,
 which seems undesirable.
-Using ''all: default'' would not solve it, as it would fail to remove
+Using ''all: revert'' would not solve it, as it would fail to remove
 the UA styles as intended.
 How can we mitigate this?