css文字下划线动画

鼠标悬停在文本上的时候触发下划线的效果，很实用的css文字下划线动画。

/* 定义动画 */
        @keyframes bgAnimation {
            0% {
                background-position: 0% 50%;
            }
 
            50% {
                background-position: 100% 50%;
            }
 
            100% {
                background-position: 0% 50%;
            }
        }

.title span {
            background: linear-gradient(to right, #d87a00, #000) no-repeat right bottom;
            background-size: 0 2px;
            transition: background-size 1s;
        }