how to apply css inside iframe\ code example
Example 1: custom iframe
<iframe width="560" height="315" src="https://www.youtube.com/embed/owsfdh4gxyc" frameborder="0" allowfullscreen></iframe>
Example 2: put html in iframe
<iframe srcdoc="<html><body>Hello, <b>world</b>.</body></html>"></iframe>