min and max width media query o only min? 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 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 3: what is a max and min width media query

/* What this query really means, is If [device width] is less than or equal to 600px, then do */
@media only screen and (max-width: 600px)  {...}

/* What this query really means, is If [device width] is greater than or equal to 600px, then do */
@media only screen and (min-width: 600px) {...}