Adding additional buttons to the WYSIWYG

I'm trying to add buttons for "Font size" and Font Color" on the WYSIWYG bar for multichoice and single choice questions.  I am using the following code and can add TAGS easily enough but I'm unable to add "FONT" related settings, does anyone please know the correct syntax for this:

function mymods_h5p_semantics_alter(&$semantics, $library_name = NULL) {
  // Check if this is the multichoice question type.
  if ($library_name !== 'H5P.MultiChoice') {
    return; // Nope, do not continue.
  }
 
  foreach ($semantics as $field) {
    // Go through list fields
    while ($field->type === 'list') {
      $field = $field->field;
    }
 
    // Go through group fields
    if ($field->type === 'group') {
      mymods_h5p_semantics_alter($field->fields, $library_name); // Check your function name!
      continue;
    }
 
    // Check to see if we have the correct type and widget
    if ($field->type === 'text' && isset($field->widget) && $field->widget === 'html') {
      // Found a field. Add support for table tags.
      if (!isset($field->tags)) {
        $field->tags = array();
      }
      $field->tags = array_merge($field->tags, array(
        'table',
        'thead',
        'tfoot',
        'tbody',
        'tr',
        'th',
        'td'
      ));
    }
  }
}