Not sure. First sentence feels a little long?

"Browsers have default styling for forms, usually shared with that of the operating system user interface (UI), making it familiar to users."

I present some alternatives for the last one as well:

* "These defaults are also highly accessible to all types of users so thought should be given to ensure that styling added does not remove any of this functionality."
* "These defaults are also highly accessible to all types of users so take care to ensure that styling added does not remove any of this functionality"
* "These defaults are also highly accessible to all types of users so ensure that styling added does not remove any of this functionality"
* "Take care to ensure that any styling added does not remove any of the native, highly accessible functionality offered by these defaults."