Third-party plugins can grant you easier access to the "essence" of your website and make inserting codes/strings easier. There are many plugins, for many purposes. For example, one of them is the Headers and Footers plugin which you may use to add code to the header and/or footer section. You may download and install it from here.
This article on Wordpress describes how to add codes safely to your Wordpress website. Basically they recommend wrapping your code in these tags:
[code language="css"]
your code here
[/code]
Note: CSS can be replaced with other languages, including actionscript3, bash, clojure, coldfusion, etc.
You may read more detailed instructions here.
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