Просто добавьте эти CSS коды.
.ui-menu-item-wrapper {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, "Noto Sans", sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji";
background-color: transparent;
border: none !important;
text-decoration: none;
}
.ui-menu-item {
display: block;
width: 100%;
padding: 0.25rem 1.5rem;
clear: both;
font-weight: 400;
color: #000;
text-align: inherit;
white-space: nowrap;
background-color: transparent;
border: 0;
}
.ui-menu-item:hover, .ui-menu-item:focus {
color: #16181b;
text-decoration: none;
background-color: #eaeaf1;
}
.ui-menu:hover .ui-menu-item-wrapper, .ui-menu-item-wrapper:hover{
background: transparent;
border: none;
}
<!DOCTYPE html>
<head>
<meta charset="utf-8">
<script src="https://code.jquery.com/jquery-3.3.1.min.js" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.js"></script>
<link rel="stylesheet" href="https://ajax.googleapis.com/ajax/libs/jqueryui/1.12.1/themes/smoothness/jquery-ui.css">
<link rel="stylesheet" type="text/css" href="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-tokenfield/0.12.0/css/bootstrap-tokenfield.css">
<link rel="stylesheet" type="text/css" href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.3.1/css/bootstrap.css">
<link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.8.2/css/all.css">
</head>
<body>
<!-- Button trigger modal -->
<button type="button" class="btn btn-primary" data-toggle="modal" data-target="#exampleModal">
Launch demo modal
</button>
<style>
.ui-menu.ui-widget.ui-widget-content.ui-autocomplete.ui-front {
z-index: 1051; // Or more
}
.token-input {
width: 25vmin !important;
}
.tokenfield .token {
height: 25px;
}
.ui-menu-item-wrapper {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, "Noto Sans", sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji";
background-color: transparent;
border: none !important;
text-decoration: none;
}
.ui-menu-item {
display: block;
width: 100%;
padding: 0.25rem 1.5rem;
clear: both;
font-weight: 400;
color: #000;
text-align: inherit;
white-space: nowrap;
background-color: transparent;
border: 0;
}
.ui-menu-item:hover, .ui-menu-item:focus {
color: #16181b;
text-decoration: none;
background-color: #eaeaf1;
}
.ui-menu:hover .ui-menu-item-wrapper, .ui-menu-item-wrapper:hover{
background: transparent;
border: none;
}
</style>
<!-- Modal -->
<div class="modal fade" id="exampleModal" tabindex="-1" role="dialog" aria-labelledby="exampleModalLabel" aria-hidden="true">
<div class="modal-dialog" role="document">
<div class="modal-content">
<div class="modal-header">
<h5 class="modal-title" id="exampleModalLabel">Modal title</h5>
<button type="button" class="close" data-dismiss="modal" aria-label="Close">
<span aria-hidden="true">×</span>
</button>
</div>
<div class="modal-body">
<input type="text" class="form-control" id="tokenfield" value=""/>
</div>
<div class="modal-footer">
<button type="button" class="btn btn-secondary" data-dismiss="modal">Close</button>
<button type="button" class="btn btn-primary">Save changes</button>
</div>
</div>
</div>
</div>
<div class="dropdown">
<button class="btn btn-secondary dropdown-toggle" type="button" id="dropdownMenuButton" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
Dropdown button
</button>
<div class="dropdown-menu" aria-labelledby="dropdownMenuButton">
<a class="dropdown-item" href="#">Action</a>
<a class="dropdown-item" href="#">Another action</a>
<a class="dropdown-item" href="#">Something else here</a>
</div>
</div>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jqueryui/1.12.1/jquery-ui.min.js"></script>
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.7/js/bootstrap.js"></script>
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-tokenfield/0.12.0/bootstrap-tokenfield.js"></script>
</body>
<script>
$('#tokenfield').tokenfield({
autocomplete: {
source: ['Test 1',
'Test 2',
'Test 3'],
delay: 100
},
showAutocompleteOnFocus: true
})
</script>
</html>