When i see your answers, i think you never verified what was the result of your network. It is a pity

It is a example, width:100px; the width can be anything you wanted, please make sure you have flushed cache after making changes.

This post wasn't about the size of the images.
When you visit a profil, before the informations of this profile, the images of the ADS are displayed

I made de change for the size of the Ads. I replaced
.ossn-ad-item .ad-image {
width:100%;
}
by
.ossn-ad-item .ad-image {
width:100px;
}
in themes\goblue\plugins\default\css\core\default.php
but nothing changed

You can change size in CSS, themes\goblue\plugins\default\css\core\default.php

.ossn-ad-item .ad-image {
    width:100px
}