/* 自定义作者头像 */
.md-author__avatar {
    background-image: url('../assets/logo.png') !important;
    background-size: cover;
    background-position: center;
}

.md-author__avatar img {
    opacity: 0;
}

/* 如果使用的是其他类名 */
.author-avatar,
.post-author img,
.article-author img {
    content: url('../assets/logo.png') !important;
}