im trying to change the color of a class on bybit exchange. the problem is that the extension stops working after reloading two times and then I have to clear my cache to get it runnig again. im pretty new to programming so yeah... :) here is the code

function btn4() {

var recent = document.getElementsByClassName("rt__head full flex");

recent[0].style.backgroundColor = "lightblue";
}
btn4();

this is my manifest file below:

  "name": "Bybit orderbook color",


"version": "1.1",
  "manifest_version": 2,

  "content_scripts": [
    {
      "matches": [ "https://www.bybit.com/trade/usdt/BTCUSDT/*" ],
      "run_at": "document_idle",
      "js": [ "background.js" ]

    }

  ],

  "permissions": [ "activeTab" ]


}