Просто добавьте ниже CSS в ваш style.css, и ваш элемент будет показан в качестве примера:
.dropdown-item {
display: block;
width: 100%;
padding: .25rem 1.5rem;
clear: both;
font-weight: 400;
color: #212529;
text-align: inherit;
white-space: nowrap;
background-color: transparent;
border: 0
}
.dropdown-item:focus,
.dropdown-item:hover {
color: #16181b;
text-decoration: none;
background-color: #f8f9fa
}
.dropdown-item.active,
.dropdown-item:active {
color: #fff;
text-decoration: none;
background-color: #007bff
}
.dropdown-item.disabled,
.dropdown-item:disabled {
color: #6c757d;
background-color: transparent
}
.dropdown-menu.show {
display: block
}
.dropdown-header {
display: block;
padding: .5rem 1.5rem;
margin-bottom: 0;
font-size: .875rem;
color: #6c757d;
white-space: nowrap
}