casper/partials/header.hbs

{{!--
Wow what the hell is going on in here even?

Ok so, several templates use this big header with a giant BG image. Nice idea, but big images
have a heavy impact on performance, so it's a good idea to make them responsive. Because we
can only get the image dynamically using Handlebars, and we can only set the image to properly
be a background image using CSS, we end up with a handful of inline styles.

If the template in question has a background image, then we render responsive image styles
for it, and apply those styles to the <header> tag. Else, we just output a <header> tag
with a `no-image` class so we can style it accordingly.
--}}

{{#if background}}

<style type="text/css">
.responsive-header-img {
    background-image: url({{img_url background size='xl'}});
}
@media(max-width: 1000px) {
    .responsive-header-img {
        background-image: url({{img_url background size='l'}});
        background-image: -webkit-image-set(
                url({{img_url background size='l'}}) 1x,
                url({{img_url background size='xl'}}) 2x
        );
        background-image: image-set(
                url({{img_url background size='l'}}) 1x,
                url({{img_url background size='xl'}}) 2x
        );
    }
}
@media(max-width: 600px) {
    .responsive-header-img {
        background-image: url({{img_url background size='m'}});
        background-image: -webkit-image-set(
                url({{img_url background size='m'}}) 1x,
                url({{img_url background size='l'}}) 2x
        );
        background-image: image-set(
                url({{img_url background size='m'}}) 1x,
                url({{img_url background size='l'}}) 2x
        );
    }
}
</style>
<header class="site-header outer responsive-header-img">

{{else}}

<header class="site-header outer no-image">

{{/if}}