CSS custom properties don't work in media queries. Custom media queries could help out here but unfortunately, they're not supported yet.
Oh snap... Something got lost. Check some dogs in the meantime!
em and strong elements are not announced by assistive technologies such as screen readers.
Hone your craft to be better than average.
Input elements of type email and file support the multiple attribute which allows entering multiple email addresses.
Use Twitter's "hidden" embed API to statically prerender Tweets on your sites.