鼠标悬停触发显示
:hover {
              background: linear-gradient(to left, #043add, #043add) left top no-repeat,
                linear-gradient(to bottom, #043add, #043add) left top no-repeat,
                linear-gradient(to left, #043add, #043add) right bottom no-repeat,
                linear-gradient(to left, #043add, #043add) right bottom no-repeat;
              /*设置大小*/
              background-size: 0.12rem 1rem, 1rem 0.12rem;
            }

默认是透明opacity: 0; 鼠标悬停触发显示
增加css3过渡效果，显示更平滑

:before {
              position: absolute;
              bottom: 0;
              left: 0;
              width: 20px;
              height: 20px;
              content: "";
              border-left: 2px solid #043add;
              border-bottom: 2px solid #043add;
              transition: all 0.6s ease;
              opacity: 0;
            }

            :after {
              position: absolute;
              top: 0;
              right: 0;
              width: 20px;
              height: 20px;
              content: "";
              border-right: 2px solid #043add;
              border-top: 2px solid #043add;
              transition: all 0.6s ease;
              opacity: 0;
            }

            :hover:before,
            :hover:after {
              opacity: 1;
            }