I tried using this solution as well since I had the same question as Roberto above. Somehow, both the form and label widths are not changing no matter what value I put for the width. Is there something else I need to be setting to make the form body wider/narrower? Here is the current setting I have in the Custom CSS tab:
I’m not sure why it is not working – it’s hard to tell without looking at it.
You must use the developer tools to inspect (right click > inspect and look at the Styles) to see what styles are actually applied to your form. Any styles that are overridden will show with a strike-through in the list.