An iFrame is actually an inline frame used inside a webpage to load another HTML document inside it, including other CSS, scripts, images and resources. A simple iframe code would look like this:

<iframe width="500" height="350" src="https://www.youtube.com/watch?v=irjFFVUgb2M" frameborder="0" allowfullscreen></iframe>

In the example given above, the iframe tag loads YouTube’s video player with the video ID provided in the code. It has other parameters defined as well, such as height, width, frameborder, etc.

We advise you to be cautious when you are asked to embed iframe code into your website. You should only embed an iframe code into your website if it is from a reliable source, and you are certain about the identity of the website.
Also, you must know that you cannot affect any styles within an iframe, as it behaves as a separate environment.