Reply To: Where to access CSS to change link, button, horizontal rule color, etc.
BuddyPress use templates and CSS which are all stored in bp-templates/bp-legacy/buddypress/
To modify them, you have to create first a child-theme and copy into it any of the files you want to modify, by respecting /path/file structure of the original /buddypress/ folder.
In brief, wp-content/themes/child-theme/buddypress/file
Most of your questions are related to CSS. You make these changes in /child-theme/style.css
To alter the searchbar, but depending of what you exactly want to do, see bp-templates/bp-legacy/buddypress/groups/index.php (similar path for members) or creating a custom function if more in-depth modification. In that case you put this function into bp-custom.php (wp-content/plugins/bp-custom.php) or into child-theme’s functions.php
More details can bee found on Codex
