To customize Bootstrap

By going to this site http://getbootstrap.com/customize/ We can customize the bootstrap by selecting the
Less files like

Common CSS

Print media styles

Typography

Code

Grid system

Tables

Forms

Buttons

Responsive utilities

Components

Glyphicons

Button groups

Input groups

Navs

Navbar

Breadcrumbs

Pagination

Pager

Labels

Badges

Jumbotron

Thumbnails

Alerts

Progress bars

Media items

List groups

Panels

Responsive embed

Wells

Close icon

JavaScript components

Component animations (for JS)

Dropdowns

Tooltips

Popovers

Modals

Carousel

jQuery plugins

Linked to components

Alert dismissal

Advanced buttons

Carousel functionality

Dropdowns

Modals

Tooltips

Popovers (requires Tooltips)

Togglable tabs

Magic

Affix

Collapse

Scrollspy

Transitions (required for any kind of animation)

Less variables

Customize Less variables to define colors, sizes and more inside your custom CSS stylesheets.

@gray-base

Scaffolding

Settings for some of the most global styles.

@body-bg 

@text-color

Typography

@font-family-sans-serif

Iconography

@icon-font-path @icon-font-name

Tables 

Buttons

Forms