文章编辑器添加一个自定义的CSS样式表

用法

<?php add_editor_style( $stylesheet ); ?>

参数：

 $stylesheet
(string/array) (可选) Path to a stylesheet file, relative to the current theme directory, or an array thereof to link multiple stylesheet files.
默认值: "editor-style.css"

If a child theme is used, both the current child and parent theme directories are considered (see Description).
As of version 3.6, http or https URLs (e.g., http://example/style.css) can be used. Root-relative URLs will not work: e.g., /editor-style.css is treated the same as editor-style.css.
Paths with a query string (e.g., editor-style?ver=…) will fail to be added. You can work around that by using the equivalent http(s) URL, e.g. , http://example/editor-style.css?ver=…. (get_stylesheet_directory_uri() and home_url() can help you build "full" URLs.)
Call get_editor_stylesheets() to see which styles have been added. 

举例：

/**
 * Registers an editor stylesheet for the theme.
 */
function wp_bootstrap_4_add_editor_styles() {
    add_editor_style( 'editor-style.css' );
}
add_action( 'admin_init', 'wp_bootstrap_4_add_editor_styles' );

参考：

http://wphun.com/f/add_editor_style