How to hide elements of an external widget on my website

I am trying to instal a chat widget in my website and I would like to hide certain elements of the chat widget.

The chat is provided by Tidio but I guess this apply to any widget.

I am specifically trying to hide a button that minimise the chat button as highlighted in the image below.

I have inspected the button and found out that button has a class exit-chat, so I run this script where I try to get the button with document.getElementsByClassName("exit-chat") however the document is somehow null. I have also tried to add a delay before getting the button but it does not work.

Here is the code I have written and here is the link to a codepen

<script src="//code.tidio.co/fouwfr0cnygz4sj8kttyv0cz1rpaayva.js" async="async"></script>
  <!-- Swap your javascript code above -->
  <script>
     (function() {
      function onTidioChatApiReady() {
        (function() {
          //code run after the widget is loaded
          window.tidioChatApi.open();
          const loading = document.getElementsByClassName("loading");
          loading[0].style.display = "none";
          const tidioo = document.getElementById("tidio-chat");
          tidioo.style.display = "display";
            
          var timeoutInSeconds = 2;
            setTimeout(function() {
                    console.log("timeout");
                const minimizee = document.getElementsByClassName("exit-chat");
                    console.log(minimizee==null);
            minimizee[0].style.display = "none";
                    minimizee[1].style.display = "none";
            }, timeoutInSeconds * 1000)
            
        })();
      }
      if (window.tidioChatApi) {
        window.tidioChatApi.on("ready", onTidioChatApiReady);
      } else {
        document.addEventListener("tidioChat-ready", onTidioChatApiReady);
      }
    })();
  </script>

 <div class="loading">
    <p>Loading...</p>
 </div>

Can you please help to understand where I get this wrong and explain how to hide that button?
Thanks!!