Your code is highlighting the entire body
, however the content inside the iFrame is not, by most browsers, considered to be in the same body
as the current document.
In short, $('body') includes everything in the page but things inside an iFrame is excluded (due to the awkward nature of iFrame).
Highlight the content by explicitly selecting it using jQuery instead.
I tend to avoid iFrame at all cost. jQuery is pretty powerful in real-time manipulation of HTML contents that I was never really forced to use an iFrame.