how to add a dark filter in css code example

Example 1: css image filter black and white

-webkit-filter: grayscale(100%); /* Safari 6.0 - 9.0 */
  filter: grayscale(100%);

Example 2: brightness css

brightness(0%)   /* Completely black */
brightness(0.4)  /* 40% brightness */
brightness(1)    /* No effect */
brightness(200%) /* Double brightness */