tinymce-docs-4x/_includes/configuration/theme-url.md

theme_url

If you are using TinyMCE themes, this option enables you to specify the location of the theme file. This is useful if you are loading TinyMCE from one URL, for example a CDN, while loading a theme on, say, a local server.

Type: String

Example:

tinymce.init({
  selector: "textarea",  // change this value according to your html
  theme_url: "/mytheme/mytheme.js"
});