Dropdown

<div class="dropdown">
    <!-- The trigger element -->
    <div class="dropdown__trigger">...</div>

    <!-- The content -->
    <div class="dropdown__content">...</div>
</div>

.dropdown {
    position: relative;
}

.dropdown__trigger {
    cursor: pointer;
}

/* Hide the dropdown's content by default */
.dropdown__content {
    display: none;

    /* Position it right below the trigger element */
    left: 0;
    padding-top: 0.25rem;
    position: absolute;
    top: 100%;

    /* It should be on the top of other elements */
    background-color: #fff;
    z-index: 9999;
}

/* Show the content when hover on the container */
.dropdown:hover .dropdown__content {
    display: block;
}