In RH10, I'm using the WebHelp to CHM converter to create my CHM output. I use my own CSS file that controls the look of my WebHelp and CHM outputs. I set up my WebHelp options to include the Show/Hide link when a topic from the CHM is called as context-sensitive. Unfortunately with my CSS applied, the Show/Hide link seems to be obscured.
Also, I tried generating the CHM using the HTML Help layout option, but the output ignores a number of entries in my CSS, which makes the display unacceptable. (I can't have separate CSSs for WebHelp and CHM.)
Finally discovered the same a few days ago and now it's styled and working great.