fixing stickyness of the date (#15964)

GitOrigin-RevId: 9bc9bc1323f944a7c57e0bb92724063d8da44e89

services/web/frontend/js/features/history/components/change-list/history-version.tsx

@@ -75,15 +75,13 @@ function HistoryVersion({
       ) : null}
       {update.meta.first_in_day ? (
         <div
-          className={classNames({
-            'version-element-within-selected ':
+          className={classNames('history-version-day', {
+            'version-element-within-selected':
               selectionState === 'withinSelected' ||
               selectionState === 'lowerSelected',
           })}
         >
-          <time className="history-version-day">
-            {relativeDate(update.meta.end_ts)}
-          </time>
+          <time>{relativeDate(update.meta.end_ts)}</time>
         </div>
       ) : null}
       <div

services/web/frontend/stylesheets/app/editor/history-react.less

@@ -91,6 +91,7 @@ history-root {
   }
 
   .history-version-day {
+    background-color: white;
     position: sticky;
     z-index: 1;
     top: 0;