/* If the viewport width <= 1000 pixels ... */
@media screen and (max-width: 1000px) {

#header {
height:140px;
}

#content {
width: 75%;
}
#sidebar {
width: 25%;
}
#sidebar .inner {
margin-right: 0;
margin-top: 0;
}
}

    /* If the viewport width <= 760pixels ... */
@media screen and (max-width: 767px) {

#header {
height:170px;
}
#sidebar {
display: none; 
clear: both;
}
#content {
width: 100%;
}
#content .inner {
margin-right: 0; 
}
<!-- #sidebar {
float: none;
clear: both;
width: 100%;
margin-bottom: 20px;
} -->
}

    /* If the viewport width <= 480 pixels ... */
@media screen and (max-width: 480px) {
body {
margin: 0;
}
#content .bloks {
width:95%;
margin:1%;
height:100%; 
}
#content .bloks img {
width:100%;
height:100%;
}
#sidebar {
display: none; /* не виден при ширине <=480 px */
clear: both;
}

#header .inner {
padding-top: 5px;
padding-bottom: 20px;
}
#header .inner, #content, #nav, #sidebar {
margin-bottom: 5px;
}
}

@media (max-width:800px) {
   .need-hide{
       display:none;
   }
}