make color darker using plain css code example
Example: how to make background more darker with css
/* makes your image darker */
background-image: linear-gradient(rgba(0, 0, 0, 0.5), rgba(0, 0, 0, 0.5)),
url(your image location)
/* makes your image darker */
background-image: linear-gradient(rgba(0, 0, 0, 0.5), rgba(0, 0, 0, 0.5)),
url(your image location)