在后台css添加

#comment-textarea {
    background-image:url(https://gitee.com/r3387/wenyu/raw/master/plk.gif);
    background-size:contain;
    background-repeat:no-repeat;
    background-position:right bottom;
    transition:all 0.25s ease-in-out 0s;
}
textarea#comment-textarea:focus{
    background-position-y:120px;
    transition:all 0.25s ease-in-out 0s;
}

原文链接：https://ysazw.cn/wl/bjk.html