ActionView::Template::Error: File to import not found or unreadable: jquery-ui/datepicker.

gem 'jquery-rails', '~> 4.3'
gem 'jquery-ui-rails', '~> 6.0'

//= require jquery3
//= require jquery-ui/widgets/datepicker

@import "jquery-ui/datepicker";
@import "jquery-ui/core";
@import "jquery-ui/theme";