Bootstrap Modal can’t be hidden (Asp.net core, C#)

I have created a .NET Core project and used a Bootstrap Modal and ajax to Edit and delete data.
But somehow my modal can’t be hidden.

here is my index file

 <a href="javascript:void(0)" class="delete" onclick="ConfirmDelete(@item.Id)">
                            <i class="material-icons" data-toggle="tooltip" title="Delete">&#xE872;</i>
                        </a>
                        <!-- Delete Modal HTML -->
                        <div id="deleteCategoryModel" class="modal fade">
                            <div class="modal-dialog">
                                <div class="modal-content">
                                    <div class="modal-header">
                                        <h4 class="modal-title">Delete Category</h4>
                                        <button type="button" class="close" data-dismiss="modal" aria-hidden="true">&times;</button>
                                    </div>
                                    <div class="modal-body">
                                        <h6 class="#modal_body"></h6>
                                        <p>Are you sure you want to delete this Category?</p>
                                        <p class="text-warning"><small>This action cannot be undone.</small></p>
                                    </div>
                                    <div class="modal-footer">
                                        <input type="button" class="btn btn-default" value="Cancel" onclick="closeDeleteModal()">
                                        <input type="button" class="btn btn-danger" value="Delete" onclick="DeleteCategory()">
                                    </div>
                                </div>
                            </div>
                        </div>

                        <input type="hidden" id="hiddenCategoryId" />

and my code jQuery:

var ConfirmDelete = function (Id) {

$("#hiddenCategoryId").val(Id);
$("#deleteCategoryModel").modal('show');

}

var DeleteCategory = function () {

var Id = $("#hiddenCategoryId").val();

$.ajax({

    type: "POST",
    url: "/Category/Delete",
    data: { id: Id },
    success: function (result) {
        $("#deleteCategoryModel").modal("hide");
        $("#row_" + Id).remove();
    }
});

}

var closeDeleteModal = function () {
$('#deleteCategoryModel').modal('hide');

}