CSS网页制作实例:有条件的添加hover样式

          #all > ul {
                list-style: none;
                float: left; width: 200px;
                padding: 0 10px 0 0;
            }
            #all a {
                        text-decoration: none;
                        display: block;
                        padding: 10px;
                        background: #900;
                        border-radius: 20px;
                        color: white;
                        text-align: center;
                        margin: 0 0 5px 0; 
 
                        -webkit-transition: all 0.2s ease;
                        -moz-transition: all 0.2s ease;
                        -o-transition: all 0.2s ease;
            }
            #all:hover a {
                        opacity: 0.2;
            }
            #all:hover ul:hover a {
                        opacity: 0.5;
            }
            #all:hover ul:hover a:hover {
                        opacity: 1;
            }