In HTML output files from R Notebooks, how do I hide the button on top-right of cells asking for hiding the code?

I have Googled about it but I am not getting what I am looking for.

I am using the R Notebooks for the first time today. In the output HTML files, at the top-right of every code-cell, there is annoying little button asking me whether I want to hide the code cells. I don't want to hide the code cell but I do want to hide this button from output HTML. How do I do this?