可重复使用的变数transition-timing-function 属性，比内置更强大ease ，ease-in ，ease-out 和ease-in-out 。

HTML

CSS

:root {

--ease-in-quad: cubic-bezier(0.55, 0.085, 0.68, 0.53);

--ease-in-cubic: cubic-bezier(0.55, 0.055, 0.675, 0.19);

--ease-in-quart: cubic-bezier(0.895, 0.03, 0.685, 0.22);

--ease-in-quint: cubic-bezier(0.755, 0.05, 0.855, 0.06);

--ease-in-expo: cubic-bezier(0.95, 0.05, 0.795, 0.035);

--ease-in-circ: cubic-bezier(0.6, 0.04, 0.98, 0.335);

--ease-out-quad: cubic-bezier(0.25, 0.46, 0.45, 0.94);

--ease-out-cubic: cubic-bezier(0.215, 0.61, 0.355, 1);

--ease-out-quart: cubic-bezier(0.165, 0.84, 0.44, 1);

--ease-out-quint: cubic-bezier(0.23, 1, 0.32, 1);

--ease-out-expo: cubic-bezier(0.19, 1, 0.22, 1);

--ease-out-circ: cubic-bezier(0.075, 0.82, 0.165, 1);

--ease-in-out-quad: cubic-bezier(0.455, 0.03, 0.515, 0.955);

--ease-in-out-cubic: cubic-bezier(0.645, 0.045, 0.355, 1);

--ease-in-out-quart: cubic-bezier(0.77, 0, 0.175, 1);

--ease-in-out-quint: cubic-bezier(0.86, 0, 0.07, 1);

--ease-in-out-expo: cubic-bezier(1, 0, 0, 1);

--ease-in-out-circ: cubic-bezier(0.785, 0.135, 0.15, 0.86);

}

.easing-variables {

width: 50px;

height: 50px;

background: #333;

transition: transform 1s var(--ease-out-quart);

}

.easing-variables:hover {

transform: rotate(45deg);

}

说明

变量是在:root 与表示文档的树的根元素匹配的CSS伪类。用HTML，:root 表示 元素，并且与选择器相同html ，只是其特异性较高。