Different Author Comment in Blogger - Cannot Detect CSS .icon.blog-author

I'm trying to make different style for author comment in my blogspot : Teknomia

I'm using stock comment (default from blogger)

I use this code :

#comments .comments-content .icon.blog-author:after{
  content: 'Admin';
  background-color: #118ff9; 
  color: #fff;
  border-radius: 3px;
}

But, Blogger can't detect this code, which identify tag for author :

.icon.blog-author:after

When I try to change my code like this :

#comments .comments-content .user a:after{
  content: 'Admin';
  background-color: #118ff9; 
  color: #fff;
  border-radius: 3px;
}

It work (all comment include my visitors comment marked as author)

I want to know how to marked author comment only (only my comment marked)