The log-in page is a WordPress page. There is a guide on how to customize it:
https://codex.wordpress.org/Customizing_the_Login_Form
The registration page is created by BuddyPress and can be modified in many ways. You’ll need to understand theme compatibility and overriding templates:
Theme Compatibility & Template Files
So you could create your own copy of buddypress/members/register.php in your theme to make big changes, or potentially hook into the action bp_before_register_page to just add some html to top of the BP page.
Best of luck.
I want to customize the login page of buddypress it is redirecting the worpdress default login age
