how to darken background image with css

1.container img {
2  filter: brightness(50%);
3}

1/* Answer to: "css darken background image" */
2
3/*
4  You can use the CSS3 Linear Gradient property along with your
5  background-image like the code shown below.
6
7  Here's a link to the CSS4 Linear Gradient property:
8  http://www.w3schools.com/css/css3_gradients.asp
9*/
10
11#landing-wrapper {
12  display: table;
13  width: 100%;
14  background: linear-gradient(rgba(0, 0, 0, 0.5), rgba(0, 0, 0, 0.5)), url('landingpagepic.jpg');
15  background-position: center top;
16  height: 350px;
17}