Login as admin and find the Customize menu on top admin bar:

Click on that, find the Additional CSS menu, open and and put this CSS code:

.wpforo-widget-content p.posttext{display:none;}
.wpforo-widget-content p.posttitle{font-size:12px; margin-bottom:3px;}
.wpforo-widget-content .postuser{font-size:12px; }
.wpforo-widget-content li{border-bottom:1px dashed #999999; margin-bottom: 7px}

Don't forget, save it using the top blue [Publish] button, then delete all caches and press Ctrl+F5 before checking.

Thank you very very much

both

This time worked !