Dropdown is a toggelable menu which allow user to choose one or mutiple items.
.dropdown-menu under ul component is used to make the dropdown list and
.dropdown-toggle is used to make the dropdown toggling on click of button.
.caret in span is used to make the arrow sign in dropdown.
.divider class is used to divide the dropdown items with thick horizontal border.
To give header in dropdown menu
.dropdown-header class is used.
In ul component
.dropdown-menu-right class is used to open the dropdown menu on right side.
.disabled class is used to make a dropdown item disabled.
.dropup class is used to open dropdownlist on upperside.