.photo_add
    {
    width:25%;
    }
    
.fit
  {
  position:relative;
  padding-top:100%;    /* 1:1 Aspect Ratio */
  }

.fit img
  {
  position:absolute;
  top:0;
  left:0;
  height:100%;
  width:100%;
  object-fit: cover;  /* adaptation contenu a son parent */
  }
  
img.youtube_play
    {
    position:absolute;
    left:50%;
    top:50%;
    z-index:2;
    margin-left:-25px;
    margin-top:-17px;
    }