Answers for "css an element inside iframe"

change element in iframe

// so you got an iframe (id="myiframe"). In that page you have an element id="theprice" and you want to change its value
// from the parent page do this in your javascript:
var iframevar = document.getElementById('myiframe');
var elmnt = iframevar.contentWindow.document.getElementById("theprice");
elmnt.innerHTML = theNewPrice;

iframe innerthtml

//Make sure to select 'top' from JS context dropdown menu in chrome devtools console

document.querySelector('iframe class/id').contentWindow.document.querySelector('body').innerHTML