What's this box around some kanji on the new dashboard?

[DollyDaydream]

You must have the Dashboard Progress Plus script installed as this is what produces the box as far as I know.

[Userscript] Dashboard Progress Plus

Dashboard Progress Plus This is a third-party script/app and is not created by the WaniKani team. By using this, you understand that it can stop working at any time or be discontinued indefinitely. [ General Script Installation instructions ] You’ll need a script host plugin like TamperMonkey [ Open Framework Installation ] [ Download / Install “Dashboard Progress Plus” ] Features: Visually indicate SRS stages of items, including Locked and Lessons Adds a “90%” ka…

It then works as @thomasmichaelwal has mentioned in his post.