I am trying to apply these CSS rules to x3 Post-ID’s but I can’t get it to work – any idea how I can?

.postid-209506, .postid-209512, .postid-209513 {
background-image: url('.jpg');
}
.postid-209506 .entry-title, .postid-209512 .entry-title, .postid-209513 .entry-title{
   display: none;
}
.postid-209506 .entry-header #entry-meta, .postid-209512 .entry-header #entry-meta, .postid-209513 .entry-header #entry-meta{
    display:none;
}