change the class that is behind the id gChatFrame

Question

Retrieve the class that has the ID "gChatFrame" in the comment system: sigComments to replace the style. hard to figure out how to get to this class to modify it. https://sibiro.ru/design.html

setTimeout(()=>{
let frame=document.querySelector('#gChatFrame');
let htmlO=frame.querySelector('#gChatFrame html');
let bodyO=frame.querySelector('#gChatFrame body');
htmlO.append(bodyO);
bodyO.append(frame);
let chatCon;
frame.append(chatCon);
chatCon=document.querySelector('.chatContainer');
document.querySelector('.chatContainer').style.cssText=`
font-family: Arial;
background: none !important;
right: 0px;
bottom: 0px;
padding: 0px;
border:none !important;
overflow: hidden;
position: relative;
margin: 5px;
border-radius: 5px;
`;
// frame.appendChild(chatCon);
frame.insertAdjacentHTML('beforeBegin',chatCon);
},3900);