tinymce-docs/_includes/configuration/importcss_selector_converter.md

importcss_selector_converter

This option allows you to override the default selector to format converter function. This allows you to parse the CSS selectors manually and produce format objects out of them. If the converter returns a false value the selector is ignored from import.

Type: String

Example: Using importcss_selector_converter

tinymce.init({
  selector: 'textarea',  // change this value according to your HTML
  plugins: 'importcss',
  content_css: '/my-styles.css',
  menubar: 'format',
  importcss_selector_converter: function(selector) {
    // Custom logic
  }
});