How can I add animation to Bootstrap dropdowns?

Question

How can I add animation to the dropdown? I assume by modifying popperConfig, but how?

At the moment dropdown-menu has a generated inline style, e.g. position: absolute; inset: 0px auto auto 0px; margin: 0px; transform: translate3d(0px, 40px, 0px);

Of course I can just add transition: translate .3s ease to it, but what if I want to change the direction or something more complex?

Answer 1

In the current example, the dm-example will be the dropdown menu that shows up.
HTML will not differ much from its Bootstrap5 examples:

    <div class="dropdown">
        <button class="btn btn-secondary dropdown-toggle" type="button" id="dropdownMenuButton1" data-bs-toggle="dropdown" aria-expanded="false">
          Dropdown button
        </button>
        <ul id="dm-example" class="dropdown-menu " aria-labelledby="dropdownMenuButton1 ">
            <li><a class="dropdown-item " href="# ">Action</a></li>
            <li><a class="dropdown-item " href="# ">Another action</a></li>
            <li><a class="dropdown-item " href="# ">Something else here</a></li>
        </ul>
    </div>

For CSS animation rules handling:
#dm-example.show - describes initial styles for the block;
#dm-example.show .dropdown-item - describes initial styles for inner items;
dm-animation - is the animation on block;
item-animation - is the animation on items.

    <!-- Animate dropdown -->
     <style>
        #dm-example.show {
            position: fixed;
            animation-name: dm-animation;
            animation-duration: 2s;
        }
        
        #dm-example.show .dropdown-item {
            margin-bottom: 0;
            animation-name: item-animation;
            animation-duration: 2s;
        }
        
        @keyframes dm-animation {
            0% {
                margin-top: 0px;
            }
            50% {
                margin-top: 25px;
            }
            75% {
                margin-top: 5px;
            }
            100% {
                margin-top: 0px;
            }
        }
        
        @keyframes item-animation {
            0% {
                margin-bottom: 0px;
            }
            50% {
                margin-bottom: 25px;
            }
            75% {
                margin-bottom: 5px;
            }
            100% {
                margin-bottom: 0px;
            }
        }
    </style>