css3过渡属性:
0 默认值 表示没有过渡效果
秒(s)、毫秒(ms) [1s = 1000ms]
/* 平滑过渡 */
transition-timing-function: ease;
/* 匀速过渡 */
transition-timing-function: linear;
/* 加速*/
transition-timing-function: ease-in;
/* 减速 */
transition-timing-function: ease-out;
/* 先加速后减速 */
transition-timing-function: ease-in-out;