The name of the UI library that is going to be in use.
The css file for bootstrap should be manually included if you use bootstrap.
Examples
MaterialDesign
<input id="datepicker" width="312" />
<script>
var datepicker = $('#datepicker').datepicker({ uiLibrary: 'materialdesign' });
</script>
Bootstrap 3
<input id="datepicker" width="220" />
<script>
$('#datepicker').datepicker({ uiLibrary: 'bootstrap' });
</script>
Bootstrap 4 Material Icons
<input id="datepicker" width="234" />
<script>
$('#datepicker').datepicker({ uiLibrary: 'bootstrap4', iconsLibrary: 'materialicons' });
</script>
Bootstrap 4 FontAwesome
<input id="datepicker" width="234" />
<script>
$('#datepicker').datepicker({ uiLibrary: 'bootstrap4', iconsLibrary: 'fontawesome' });
</script>
Bootstrap 5 Material Icons
<input id="datepicker" width="234" />
<script>
$('#datepicker').datepicker({ uiLibrary: 'bootstrap5', iconsLibrary: 'materialicons' });
</script>
Bootstrap 5 FontAwesome
<input id="datepicker" width="234" />
<script>
$('#datepicker').datepicker({ uiLibrary: 'bootstrap5', iconsLibrary: 'fontawesome' });
</script>