Hello @ChungAsip ,
It looks like you already spoke with a chat agent regarding this issue. For the sake of visibility, I also wanted to make sure some insight was shared here.
It seems the issue could be related to a number of issues related to browser font sizes / zooming, in addition to an odd, sporadic glitch with the legacy template builder. Is the issue also occurring in the current editor? It may be worth trying in that editor to see if the issue can be alleviated by switching over. Otherwise, if the issue is also occurring in the current editor, then it'd be indicating an issue with the way your browser is displaying the library sub-window.