Currently there is "Toggle read/unread = m", which toggles and
then goes to the next item.
Having the opposite operation available is handy, especially when adding
new feeds and going through them from oldest to newest posts.
It seems natural to map 'M' (= shift + 'm') for this action.
Closes https://github.com/miniflux/v2/issues/1352
If the application is hosted behind a CDN like Cloudflare,
then all custom stylesheets is be the same for all users.
The random query string prevent the CDN to cache this.
