cf http://wordpress.org/support/topic/twenty-fourteen-theme-not-full-width-for-high-resolution-monitors
et ajouter le css:
.site, .site-header { max-width: 100%; } .site-content .entry-header, .site-content .entry-content, .site-content .entry-summary, .site-content .entry-meta, .page-content { /* Original max-width: 474px */ max-width: 90%; margin-right: 10px; } .hentry { max-width: 100%; }