Handling different client and server content - not showing initial render

In the hydrateRoot page, it is mentioned that
"This way the initial render pass will render the same content as the server, avoiding mismatches, but an additional pass will happen synchronously right after hydration."

which means that the initial render on the playground should show "Is Server", but it shows directly "Is Client" which is very confusing for learners and doesn't show the real behavior.
I tired opening the sandbox in external window, and it indeed shows "Is Server" first and then changing to "Is Client" as expected.

In the Website:

In The sandbox (using the fork button):

從 hydrateRoot 頁面中嵌入的 playground 開始，並將其行為與透過 fork 按鈕開啟的外部 sandbox 進行比較。重現該範例，並追蹤 playground 如何處理 hydration 及其初始渲染。完成標準是：嵌入的範例先短暫顯示 "Is Server"，然後變為 "Is Client"，與文件所述的行為一致。