A dropdown menu is a toggleable menu that allows the user to choose one value from a predefined list
The .dropdown-divider class is used to separate links
inside the dropdown menu with a thin horizontal border
The .dropdown-header class is used to add headers inside
the dropdown menu
The .active,.disable class is used to add headers inside
the dropdown menu
To right-align the dropdown, add the .dropdown-menu-end class to the element with
.dropdown-menu
The .dropup class makes the dropdown menu expand upwards
instead of downwards