Remove a PostCSS plugin used to workaround bugs in the `flex` CSS
property. Most of these bugs are no longer relevant and only affected
ancient browsers like IE 10 or 11.
https://github.com/philipwalton/flexbugs
Don't include fallback CSS properties for CSS variables. Before we
generated CSS like this:
a.tag-type-1 {
color: #c00004;
color: var(--artist-tag-color);
}
Now we generate CSS like this:
a.tag-type-1 {
color: var(--artist-tag-color);
}
This means that support for CSS variables is now required for colors to
work properly. All major browsers have supported CSS variables since
2016-2017.
