Magazine Pro - Change Full Width on Desktop to 800px (75%) and Return Mobile 840px to 100%

additional.css

/* Make Full Width Content 800px or 75% on Desktop Only */
.full-width-content .content {
    width: 70%;
    margin: 0 auto;
    float: none;
}

/* Return Full Width Content to 100% on Media Query 840px */
@media only screen and (max-width: 840px) {
	
.full-width-content .content {
    width: 100%;
}
}