Easy conditional loading of assets with css and javascript

conditional content

/* THE CSS */
@media all and (min-width: 45em) {
    body:after {
        content: 'widescreen';
        display: none;
    }
}

// THE JS
var size = window.getComputedStyle(document.body,':after').getPropertyValue('content');

if (size == 'widescreen') {
    // Load some more content.
}