But I have seen so many websites have changed their code with the help of HTML (table, tr, td...), they did not touch adsense code...with the help of HTML,CSS they changed the look and feel means they blend the add...Is it ok?
You can change the text of your own sites content, but not use any method to change the text font or the font size of the actual adsense code. Premium publisher can make changes to the adsense format (needs to be approved by google) but you have to have over 10 million pages views a month to become a premium publisher. You should really read the adsense tos so you don't try something by mistake that will get your account banned.