html multi select value from datalist to a single html textbox

https://github.com/selectize/selectize.js/fork

above is multi select from the datalist to the single textbox. I want this function working on my mvc/razor/c# web form.
however I do not like above selectize because it has css that make my own css website having some issues.

Do you know how to do select multiple value from html datalist to a single textbox (in javascript)?