Basic dropdown
Wrap the dropdown’s toggle(your button or link) and the dropdown menu within .dropdown
Dropdown outlined
Add class .btn-outline-{color}to the button inside .dropdown
Split button dropdowns
Wrap two buttons in .btn-groupand add .dropdown-toggle-splitto the toggling button
Icon dropdowns
Replace button with icon buttons
Dropup variation
Add class .dropup
Dropdown sizes
Add class .btn-{size}to dropdown buttons