Hi, just wondering if some others ran into this. I just started the book and cdnjs.cloudflare provided Bootstrap 4, instead of 3. I understand that it is under beta, but I went ahead with using it. My output displayed in the browser didn’t quite match. It looks as if the class (.panel and .panel-body) was removed and is replaced by (.card and card-block).
It will look similar to the book using the new classes.
Also, the button styling is different also. You can use (btn btn-secondary) to get the white background.
You can use the Bootstrap v4 docs linked below.
Panels have been change to Cards. Using .card and .card-block are comparable to .panel and .panel-body. The buttons can be styled as you said. I think you can just use .btn for a default button.
https://cdnjs.com/libraries/twitter-bootstrap/3.3.7 is the CDN for the referenced version of Bootstrap.