发不了全部代码，只能发这一部分了

            /*任务二、设置缩略图形状*/
            a::after{
            content:"";
            display: block;
            height: 120px;
            width: 120px;
            border: 5px solid #fff;
            border-radius: 50%;
            position: absolute;
            left: 50%;
            margin-left: -60px;
            z-index: 9999;
            top: -80px;
            }
            /*任务三、设置缩略图背景图像*/
            li:nth-of-type(1) a::after{
            background: url(http://www.w3cplus.com/demo/css3/CSS3Fullbackground/sbg1.jpg) no-repeat center;
            }
            li:nth-of-type(2) a::after{
            background: url(http://www.w3cplus.com/demo/css3/CSS3Fullbackground/sbg2.jpg) no-repeat center;
            }
            li:nth-of-type(3) a::after{
            background: url(http://www.w3cplus.com/demo/css3/CSS3Fullbackground/sbg3.jpg) no-repeat center;
            }
            li:nth-of-type(4) a::after{
            background: url(http://www.w3cplus.com/demo/css3/CSS3Fullbackground/sbg4.jpg) no-repeat center;
            }
            li:nth-of-type(5) a::after{
            background: url(http://www.w3cplus.com/demo/css3/CSS3Fullbackground/sbg5.jpg) no-repeat center;
            }
            /*任务四、给缩略图添加蒙板效果*/
            a::before{
            content:"";
            display: block;
            height: 120px;
            width: 120px;
            border: 5px solid #fff;
            border-radius: 50%;
            position: absolute;
            left: 50%;
            margin-left: -60px;
            z-index: 99999;
            top: -80px;
            background: rgba(0,0,0,0.3);
            }
            /*任务五、鼠标悬浮时，修改缩略图蒙板透明度*/
            a:hover::before{
            opacity:0;
            }
            /*任务六、点击综略图，切换背景图*/
            /*背景图从左向右出现*/
              .slideLeft:target{
              z-index: 100;
              -webkit-animation-name: slideLeft;
              -webkit-animation-duration: 1s;
              -webkit-animation-iteration-count: 1;
              -moz-animation-name: slideLeft;
              -moz-animation-duration: 1s;
              -moz-animation-iteration-count: 1;
              -ms-animation-name: slideLeft;
              -ms-animation-duration: 1s;
              -ms-animation-iteration-count: 1;
              -o-animation-name: slideLeft;
              -o-animation-duration: 1s;
              -o-animation-iteration-count: 1;
              animation-name: slideLeft;
              animation-duration: 1s;
              animation-iteration-count: 1;
            }
            /*背景图从下向上出现*/
              .slideBottom:target{
              z-index: 100;
            
              -webkit-animation-name: slideBottom;
              -webkit-animation-duration: 1s;
              -webkit-animation-iteration-count: 1;
              -moz-animation-name: slideBottom;
              -moz-animation-duration: 1s;
              -moz-animation-iteration-count: 1;
              -ms-animation-name: slideBottom;
              -ms-animation-duration: 1s;
              -ms-animation-iteration-count: 1;
              -o-animation-name: slideBottom;
              -o-animation-duration: 1s;
              -o-animation-iteration-count: 1;
            animation-name: slideBottom;
              animation-duration: 1s;
              animation-iteration-count: 1;
            }
            /*背景图由小到大出现*/
              .zoomIn:target{
              z-index: 100;
              -webkit-animation-name: zoomIn;
              -webkit-animation-duration: 1s;
              -webkit-animation-iteration-count: 1;
              -moz-animation-name: zoomIn;
              -moz-animation-duration: 1s;
              -moz-animation-iteration-count: 1;
              -ms-animation-name: zoomIn;
              -ms-animation-duration: 1s;
              -ms-animation-iteration-count: 1;
              -o-animation-name: zoomIn;
              -o-animation-duration: 1s;
              -o-animation-iteration-count: 1;
              animation-name: zoomIn;
              animation-duration: 1s;
              animation-iteration-count: 1;
            }
            
            /*背景图由大到小出现*/
              .zoomOut:target{
              z-index: 100;
              -webkit-animation-name: zoomOut;
              -webkit-animation-duration: 1s;
              -webkit-animation-iteration-count: 1;
              -moz-animation-name: zoomOut;
              -moz-animation-duration: 1s;
              -moz-animation-iteration-count: 1;
              -ms-animation-name: zoomOut;
              -ms-animation-duration: 1s;
              -ms-animation-iteration-count: 1;
              -o-animation-name: zoomOut;
              -o-animation-duration: 1s;
              -o-animation-iteration-count: 1;
              animation-name: zoomOut;
              animation-duration: 1s;
              animation-iteration-count: 1;
            }
            
            /*背景图旋转出现*/
              .rotate:target{
              z-index: 100;
              -webkit-animation-name: rotate;
              -webkit-animation-duration: 1s;
              -webkit-animation-iteration-count: 1;
              -moz-animation-name: rotate;
              -moz-animation-duration: 1s;
              -moz-animation-iteration-count: 1;
              -ms-animation-name: rotate;
              -ms-animation-duration: 1s;
              -ms-animation-iteration-count: 1;
              -o-animation-name: rotate;
              -o-animation-duration: 1s;
              -o-animation-iteration-count: 1;
              animation-name: rotate;
              animation-duration: 1s;
              animation-iteration-count: 1;
            }
            /*任务七、设置不显示的背景图层级*/
            /* Not Target */
            
              .bg:not(:target){

                -webkit-animation-name: notTarget;
                -webkit-animation-duration: 1s;
                -webkit-animation-iteration-count: 1;
                -moz-animation-name: notTarget;
                -moz-animation-duration: 1s;
                -moz-animation-iteration-count: 1;
                -ms-animation-name: notTarget;
                -ms-animation-duration: 1s;
                -ms-animation-iteration-count: 1;
                -o-animation-name: notTarget;
                -o-animation-duration: 1s;
                -o-animation-iteration-count: 1;
                animation-name: notTarget;
                animation-duration: 1s;
                animation-iteration-count: 1;
              
              }