I would like to know what is the best approach, based on good programming practices to show an external web page (say Facebook or Twitter) on my web site while being able to modify the HTML and CSS before showing it.

I know that I could use an iFrame however based on some opinions the iFrame does not seem to be a good programming practice (width issues, ugly scrollbars, etc).

Is there a better approach?

Update: Question was put on "too broad", in order to limit the possible answers I would like to know if it possible to change the CSS (and only CSS) of an iFrame, the user Muhammad Umer commented that it would be possible but provided no more details. Someone knows how to achieve this?