how to use media screen in css code example

Example 1: media query min and max

/* Max-width */
@media only screen and (max-width: 600px)  {...}

/* Min-width */
@media only screen and (min-width: 600px)  {...}

/* Combining media query expressions */
@media only screen and (max-width: 600px) and (min-width: 400px)  {...}

Example 2: css media screen

@media (max-width: 991px){
    .mobile{
        display: block;
    }
}