BuddyPress.org

I have tried to add BuddyPress to my child-theme.
My object is to change the layout of the register and activate form.

So I have created the following folder structure:
\wp-content\themes\child-theme\buddypress\members\

In this folder I placed two files:
index-register.php = same content as \wp-content\plugins\buddypress\bp-themes\bp-default\registration\index-register.php
index-activate.php = same content as \wp-content\plugins\buddypress\bp-themes\bp-default\registration\index-activate.php

This seems to work, but the layout of the forms is completely wrong, all input boxes are not aligned etc. So then I checked this forum and saw that it might be a good idea to import a stylesheet from buddypress in the child-theme folder.
So I added the following line to \wp-content\themes\child-theme\style.css

@import url( ../../plugins/buddypress/bp-themes/bp-default/_inc/css/default.css );

This fixes the aligning problem, but totally destroys the full width layout of the site.
The sidebard is destroyed and the background color is wrong etc. etc.

Is there a way to edit the register and activate form with only overrides, and leave the default styling in tact?

Any help appreciated!