<button type="buttonclass="navbar-toggle collapseddata-toggle="collapsedata-target="#navbararia-expanded="falsearia-controls="navbar"learning log topics {if user is_authenticated %hello{user username }log out {else %register log in {endif %the first element is the opening tag the body of an html file contains the content users will see on page at is element that indicates the navigation links section of the page everything contained in this element is styled according to the bootstrap style rules defined by the selectors navbarnavbar-defaultand navbar-static-top selector determines which elements on page certain style rule applies to at the template defines button that will appear if the browser window is too narrow to display the whole navigation bar horizontally when the user clicks the buttonthe navigation elements will appear in dropdown list the collapse reference causes the navigation bar to collapse when the user shrinks the browser window or when the site is displayed on mobile devices with small screens at we set the project' name to appear at the far left of the navigation bar and make it link to the home pagebecause it will appear on every page in the project at we define set of links that lets users navigate the site navigation bar is basically list that starts with yand each link is an item in this list ( to add more linksinsert more lines using the following structuretitle styling and deploying an app