[css-ui] Fix typo

Author: bangseongbeom

css-ui-4/Overview.bs

@@ -1736,7 +1736,7 @@ at least the various button-like variants of <{input}>.
 For compatibility with legacy content,
 UAs that support 'user-select' must also support ''-webkit-user-select'' as an alias.
 
-Note: The details of the aliasing aliasing mechanism is intentionally left up to the UA.
+Note: The details of the aliasing mechanism is intentionally left up to the UA.
 Making ''-webkit-user-select'' a shorthand property of 'user-select'
 is known to be an effective approach,
 and new implementers should consider it.