<iframe id="quraniframe" width="100%" height="1100px" src="https://quran.com/1?locale=fa" frameborder="0"></iframe>

so I have this frame on my main page

in the quran.com has a div with footer class so I want to change those style properties so I found these JavaScript code's but that's no effect

var iframe = document.getElementById("quraniframe");
var elmnt = iframe.contentWindow.document.getElementsByClassName("footer");