Bootstrap Tutorial For Beginners - 12 | Bootstrap Jumbotron Class | Bootstrap Page-Header Class
У вашего броузера проблема в совместимости с HTML5
Bootstrap Jumbotron Classes :
1) What is Jumbotron?
2) What Is page-Header?
3) How to write Jumbotron class in bootstrap?
4) How to write code for jumbotron with background responsive Image in bootstrap?
Jumbotron:
A jumbotron indicates a big box for calling extra attention to some special content or information.
A jumbotron is displayed as a grey box with rounded corners. It also enlarges the font sizes of the text inside it.
.Page-header:
The .page-header class adds a horizontal line under the heading (+ adds some extra space around the element):