The brightness()CSS function applies a linear multiplier to the input image, making it appear brighter or darker. Its result is a <filter-function>.
The brightness of the result, specified as a <number> or a <percentage>. A value under 100% darkens the image, while a value over 100% brightens it. A value of 0% will create an image that is completely black, while a value of 100% leaves the input unchanged. The lacuna value for interpolation is 1.
brightness(0%) /* Completely black */
brightness(0.4) /* 40% brightness */
brightness(1) /* No effect */
brightness(200%) /* Double brightness */