transition-timing-function 语法： transition-timing-function：linear | ease | ease-in | ease-out | ease-in-out | cubic-bezier(, , , )[ ,linear | ease | ease-in | ease-out | ease-in-out | cubic-bezier(, , , ) ]* 默认值：ease 取值： linear： 线性过渡。等同于贝塞尔曲线(0.0, 0.0, 1.0, 1.0)