Responsive Author Style in BBpress?

I would like change responsive design author of forum section which I attached screenshots. I tried some of code but didn't worked. Here is the code

#bbpress-forums li.bbp-body div.bbp-topic-author,
  #bbpress-forums li.bbp-body div.bbp-reply-author {
    -ms-flex-align: start;
        align-items: flex-start;
    width: 100%;
    margin: 0 0 16px;
    padding: 0 0 16px;
    border-bottom: 1px solid var(--color-divider);
    box-sizing: border-box;
  }
  .vikinger-forum-reply-author {
    -ms-flex-align: start;
        align-items: flex-start;