The question is "hide" or illegible. With CSS you can hide something by not showing it. However, if someone reading the source code of your HTML page he, she or a computer bot can simply read the hidden information.
There are several solutions:
- The intended program way is that you save the changes without publishing the page. The problem with this is that you cannot make a necessary change in the production page without also publishing the "hidden" information
- You make a test page from the published page. This is where you add new information. When you're done, copy the changes (text or widgets) to the published production page.
- You save the published production page as an HTML file and you add the changes in an HTML editor. When you are satisfied, copy the changes to the production page.
- You write the changes in an HTML editor and save them in an HTML file. If you are satisfied, add the information to the production page
By the way, it's very easy to first try things out in a free "What You See Is What You Get" (WYSWYG) editor. If you are satisfied, copy the HTML/CSS code into an Edit Rich Text. Then you view the end result in preview mode. As long as you don't publish, nobody can see the result. The WYSWYG editor code can be saved and reused if you really want to implement the changes.