@media screen and(max-width: 767px) code example

Example 1: css media query

/* BOOSTRAP MEDIA BREAKPOINTS */
/* Small devices (landscape phones, 576px and up) */
@media (min-width: 576px) {  
  .selector {
  	background-color:#f00;
  }
}
/* Medium devices (tablets, 768px and up) The navbar toggle appears at this breakpoint */
@media (min-width: 768px) {}
/* Large devices (desktops, 992px and up) */
@media (min-width: 992px) {}
/* Extra large devices (large desktops, 1200px and up) */
@media (min-width: 1200px) {}

Example 2: css media screen

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