CSS > Media Query2

mediaquery.css

/**
 * <meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=no, minimum-scale=1.0, maximum-scale=1.0" />
 **/

#foo {
    margin: 0 auto;
    min-width: 769px;
    max-width: 980px;
}
#bar {
    /* ..... */
}
#baz {
    /* .... */
}

@media only screen (max-width:321px) and (max-width:768px) {
#foo {
    min-width: 100%;
    max-width: 100%;
}
#bar {
    /* ..... */
}
#baz {
    visibility: hidden;
}

@media only screen and (max-width:320px) {
#foo {
    min-width: 100%;
    max-width: 100%;
}
#bar {
    visibility: hidden;
}
#baz {
    visibility: hidden;
}
}