customize user login Drupal 8

Hello,

I would like to customize my user login page and register but I don’t know how to do this with Drupal 8.

I have been searching on internet and I found this link : https://www.drupal.org/docs/7/theming/overriding-themable-output/customizing-and-overriding-user-login-page-register-and

But this is for Drupal 6 and 7, anyone can tell me what’s different from D7 ?

Thank you, I’m a novice so don’t use technical terms.

LD 

Drupal version: 


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