I have a question, Rated 5 out of 5 stars

How to put a style to an element inside iframe.
for example all apps on facebook are in iframe and i can't change anything to those, how to do it.

And another thing,
how to delete a style.
For example an element has "position: relative", but i don't want this how to delete this

This review is for a previous version of the add-on (1.3.2). 

Things inside iframes should be referenced based on the iframe's address. For example, if Facebook shows an iframe sourced from somedomain.com, your style would need to apply to somedomain.com for it to affect the iframe.

To remove existing styles, you simply need to set them back to the default value. The default for "position" is "static".