I use an Iframe with an external API, which I don't control. My goal is to add Javascript code in my Website, to change the style of a few elements in the Iframe. First I considered using
document.getElementById(iframeId).contentWindow.document.getElementById(elementId);
but I soon recognized that it will not be successful because I am getting security issues. I tested a bit and found out when I inspect the element in the Iframe, which I want to change, I am able to get the element simply by using:
document.getElementById(elementId);
I don't understand. Why does this technique only work when I inspect the correct element first? And is there any way I can use this trick for my normal JS backend?