grayscale()

filter: grayscale(0);

filter: grayscale(0.2);

filter: grayscale(60%);

filter: grayscale(1);

<section id="default-example">
  <img
    class="transition-all"
    id="example-element"
    src="/shared-assets/images/examples/firefox-logo.svg"
    width="200" />
</section>

grayscale(0)     /* 无效果 */
grayscale(.7)    /* 70% 灰度 */
grayscale(100%)  /* 灰度最大 */