Is it possible to change styles in free version of Rocket.chat?

For example I need to change color of support agent name to black, but I don’t have such ability from admin panel. Custom css don’t work. So maybe i can do it with “important flag” or something like this.

problem

This is code of my iframe:

'use client';
import React from 'react';

export const Support = () => {
  return (
    <div>
      <h1 className="text-4xl font-semibold mb-10">Поддержка</h1>

      <iframe
        src="https://chat.blabla.lt/livechat?mode=popout"
        title="Chat"
        frameBorder="0"
        scrolling="no"
        style={{ width: '100%', height: '800px', zIndex: '1300' }}
      ></iframe>
    </div>
  );
};