The Bootstrap navigation bar
The Bootstrap navigation bar is one of the components that is used on the majority of sites using the Bootstrap framework. The navbar functions as a navigation header in your sites and will collapse on smaller devices showing only an icon menu, using the Bootstrap Collapse plugin. It is ideally suited to include site branding and navigation.
Basic navbar
A basic navigation bar consists of the website logo or brand name, navigation menu, and options for toggling behavior on smaller devices. A basic Bootstrap navigation bar might look similar to this:

The preceding navigation bar consists of an <a> element containing the site logo, with a class name of .navbar-brand. It also contains a <ul> element, whose class name is set to .nav navbar-nav. Each <li> child element's class name is set to .nav-item. The full HTML markup required to create the navigation bar is listed here:
<nav class="navbar navbar-full navbar-dark bg-primary"...