css background darker

body{
 background:
        /* top, transparent black, faked with gradient */ 
        linear-gradient(
          rgba(0, 0, 0, 0.7), 
          rgba(0, 0, 0, 0.7)
        ),
        /* bottom, image */
        url(https://images.unsplash.com/photo-1614030424754-24d0eebd46b2);
    }
 Run code snippet

body {
    display: grid;
    place-items: center;
    height: 100vh;
}
div {
    width: 50vw;
    height: 50vh;
    background: linear-gradient(to bottom right, #55566a, #282834);
    border-radius: 10px;
}