.btn btn-default
class used to give transparent colour to button..btn btn-primary
class is used to give blueish colour to button..btn btn-success
is used to give the greenish colour to button..btn btn-info
class is used to give the skyblue colour to button..btn btn-warning
class is used to give the yellow colour to the button..btn btn-danger
class is used to give red colour to the button.