In the project iView-Admin, any page, such as join-page.vue adding < BackTop > < / BackTop >, is invalid?

in the project iView-Admin,
any page, for example, join-page.vue adds < BackTop > < / BackTop >
page height is set to 2000px, and other components of Vue.use (iView), can be introduced into main.js, but BackTop is invalid, so solve?

Nov.24,2021
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