[BUG] element does not support textbox children

config.rasi

configuration {
	location: 0;
	yoffset: 0;
	xoffset: 0;
  timeout {
      action: "kb-cancel";
      delay:  0;
  }
  filebrowser {
      directories-first: true;
      sorting-method:    "name";
  }
}

theme.rasi

/**
 * rofi -dump-theme output.
 * Rofi version: 1.7.5
 **/
* {
    background-color: Black;
    text-color:       White;
}
element {
    children: [ "element-text","textbox-foo" ];
}
textbox-foo {
    background-color: Green;
    content:          "foo";
}