# wpforo-wrap .wpforo-content {width: 73%; }
# wpforo-wrap .wpforo-right-sidebar {width: 24%;}

Now I have removed the instructions and everything seems to work.
Strange though ..

My theme is absolutely "Mobile-Friendly" and has never given me problems.

You can always test it using the WP Customizer setting by going to 

1. WP Dashboard,
2. Appearance
3. Customize

then you can see your changes BEFORE you publish. So in case there are mistakes, then you can just revert back to the former state of your forum or website, by exiting the page without hitting the "Publish" button at the top right.

Hope that helps. :-)

My dear Sofy ...

I understood the problem. I made another change to the CSS and the same thing happened: when I come back to the page the change is no longer visible and I have to do CTRL-F5 to reactivate it.
The "fault" is from Chrome. I have indeed tested with another browser and everything works.
What can be done ?
Bye thank you
Roberto

Hi @finalcut - I hope this post for you does not disappear again (my previous one disappeared). I checked your website and this is what shows. You might have changed too many things on the Custom CSS Code that it affected your entire forum layout. (The images will be attached at the bottom of this post) .

What can be done ?

It might be faster to fix if you

1) Go into your wpForo Custom CSS Code, and remove all the codes there (that caused the attached resulting images )  and start again with this.

2) On your Wordpress Forum page, just put the wpforo shortcode, like so, on the HTML tab (not the visual tab):

<br>

<br> 

3) I am not certain if you are wanting the group picture at the bottom of the forum page, or at the top of the forum page.

4) But just copy the code below, also on your Wordpress Forum Page, and put it on top of your wpForo shortcode, or below the wpforo shortcode, where ever you want the photo to appear.  So your Wordpress Forum Page HTML code would  look like this: 

<br>

<br>

<div class="background background-image" style="background-image: url(https://valledeicavalieri.it/wp/wp-content/uploads/2018/11/SfondoFORUM3-e1548672857726.jpg);max-width:100%;height:600px;filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(src='https://valledeicavalieri.it/wp/wp-content/uploads/2018/11/SfondoFORUM3-e1548672857726.jpg', sizingMethod='scale');-ms-filter:'progid:DXImageTransform.Microsoft.AlphaImageLoader(src='https://valledeicavalieri.it/wp/wp-content/uploads/2018/11/SfondoFORUM3-e1548672857726.jpg', sizingMethod='scale')';" data-imgwidth="100%">
</div>

<div class="fusion-title-sc-wrapper" style="">
<div class="fusion-title title fusion-sep-none fusion-title-center fusion-title-size-two" style="margin-top:0px;margin-bottom:0px;">
<h2 class="title-heading-center" style="color:#fff;font-size:30px;line-height:36px;">questo è il forum ufficiale della Cooperativa Valle dei Cavalieri</h2>
</div> </div>

(Do not translate the code, since it is in English), I think the front end code is in English and can be translated, I am just not certain whether the code itself can be translated, maybe the wpForo Team can clarify that).

Hope this helps. You have a nice website and a working Forum will look great on it too! Buona fortuna e Dio benedica te e la tua cooperativa! :-)

I understood the problem. I made another change to the CSS and the same thing happened: when I come back to the page the change is no longer visible and I have to do CTRL-F5 to reactivate it.
The "fault" is from Chrome. I have indeed tested with another browser and everything works.
What can be done ?
Bye thank you
Roberto

Everything works fine. Watch the video below. You just need to click CTRL+F5 on the frontend to load new style, browser cache doesn't load new changes. 

https://www.screencast.com/t/c43gdWAC2O