The transition-timing-function CSS property sets how intermediate values are calculated for CSS properties being affected by a transition effect.
/* Keyword values */
transition-timing-function: ease;
transition-timing-function: ease-in;
transition-timing-function: ease-out;
transition-timing-function: ease-in-out;
transition-timing-function: linear;
transition-timing-function: step-start;
transition-timing-function: step-end;
/* Function values */
transition-timing-function: steps(4, jump-end);
transition-timing-function: cubic-bezier(0.1, 0.7, 1.0, 0.1);
/* Steps Function keywords */
transition-timing-function: steps(4, jump-start);
transition-timing-function: steps(10, jump-end);
transition-timing-function: steps(20, jump-none);
transition-timing-function: steps(5, jump-both);
transition-timing-function: steps(6, start);
transition-timing-function: steps(8, end);
/* Multiple timing functions */
transition-timing-function: ease, step-start, cubic-bezier(0.1, 0.7, 1.0, 0.1);
/* Global values */
transition-timing-function: inherit;
transition-timing-function: initial;
transition-timing-function: unset;Source: https://developer.mozilla.org/en-US/docs/Web/CSS/transition-timing-function