How to realize the select an element on the page function of AntDesign official website

there is an icon in the lower right corner of AntDesign"s official website, in which there is a function of select an element on the page.
A dotted frame is displayed outside the element of mouse hover. how is this realized?
as shown in the following figure
clipboard.png

Mar.12,2021

register the mouseenter event with document. When you mouse over the element, add a border to the element

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