Can I use custom HTML, CSS and Scripts in Website Builder?

I would like to be able to use Custom HTML in the Description field of the Products of my Store.  Can I use custom CSS, HTML and JavaScripts from Website Builder?  I want to be able to add CSS, and Scripts globally for a Site, then I want to write HTML5 or CSS3 code in a custom element, and within the Decription and Blurb fields for Products.