CSS

darken image css

.container img {
  filter: brightness(50%);
}

make image darker in css

#myimage {
    filter: brightness(50%);
}

darken image css

#image {
	background: linear-gradient( rgba(0, 0, 0, 0.5), rgba(0, 0, 0, 0.5) ), url('landingpagepic.jpg');
}