add_editor_style()

add_editor_style() — Adds callback for custom TinyMCE editor stylesheets. The parameter $stylesheet is the name of the stylesheet, relative to the theme root. It also accepts an array of stylesheets. It is optional and defaults to ‘editor-style.css’. This function automatically adds another stylesheet with -rtl prefix, e.g. editor-style-rtl.css. If that file doesn’t exist, it is removed before adding the stylesheet(s) to TinyMCE. If an array of stylesheets is passed to add_editor_style(), RTL is only added for the first stylesheet. Since version 3.4 the TinyMCE body has .rtl CSS class.

Inputs: $stylesheet (array|string): Optional. Stylesheet name or array thereof, relative to theme root. Defaults to ‘editor-style.css’