题解 | #点击按钮隐藏元素#

.box {
                width: 100px;
                height: 100px;
                border: solid 1px black;
                /*补全代码*/
                position:relative;
            }
            .btn{
                 width: 20px;
            height: 20px;
            background-color: red;
            /*补全代码*/
            position: absolute;
            right: -10px;
            top: -10px;
            text-align:center;
             line-height:20px;
            }


       
            var btn = document.querySelector('.btn');
            var box = document.querySelector('.box');
            btn.onclick = function(){
                // 补全代码
                box.style.display = "none";
            }