Getting Started With Bootstrap 4, Part 4: Spacing Elements
У вашего броузера проблема в совместимости с HTML5
In the fourth video of our "Getting Started with Bootstrap 4" series, “Spacing Elements," CodeTime instructor Pete Medina discusses how to use Bootstrap's margin and padding spacing classes move things around the page. Users will be using these a lot going forward as they can really change the appearance of a page’s elements.