Back button look bootstrap which one to use?

1. How to add back button in Bootstrap?
2. Which class is used for a default yellow background button?

How to add back button in Bootstrap?

Below you have a working example. I used the code from the link you provided. What I did was the following: added two back buttons => <button type="button" >Back</button>

Which class is used for a default yellow background button?

Using one of the default modifier classes will change the color of the text and background color of your buttons. .Btn-danger will make the button red and font white, while . btn-warning will make the button yellow and font black, and so on.