#wrapper {width:95%;  margin: 0 auto; }

#header {width:100%; }

#content {width:100%; }

#sidebar {width:100%; }

#footer {width:100%; }

// Small devices (landscape phones, 576px and up)

@media (min-width: 576px) {

// Medium devices (tablets, 768px and up)

@media (min-width: 768px) {

#wrapper {width:90%;  margin: 0 auto; }

#content {width:70%; float:left; }

#sidebar {width:30%; float:right; }

// Large devices (desktops, 992px and up)

@media (min-width: 992px) { ... }

}

// Extra large devices (large desktops, 1200px and up)

@media (min-width: 1200px) {

#wrapper {width:90%;  margin: 0 auto; }

}