Inserting html into the current tab through chrome extention?

I am trying to insert some extra code into the current tab page in chrome using an extension i.e add a submit button on top o开发者_StackOverflowf the page. Where does this go? and how would I initialize every page like this?

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If you put this in your manifest.json,

"content_scripts": [{
  "matches": ["<all_urls>"],
  "js": ["example.js"],
  "css": ["example.css"]
}]

then example.js and example.css will be injected into every page you visit. See http://code.google.com/chrome/extensions/content_scripts.html for more information.