I can't seem to find a good tutorial online for this. I created a html page that when preview (on my hard drive), in FF, I get a red box of "1" on the right end above the windows status bar. When I hoover over it, tooltip says "1 error 2 warnings, click to toggle the developer tools".
I click on it and it changes scrren, please see attached. It hightlights Style Edior but I don't see where is the error or warning or related messages.
Appreciate someone can point me to how to get to the errors or a good tutorial for the dev tool, thank you.