Use `flexbox: 'no-2009'` or postcss-flexbugs-fixes to fix Flexbox issues

[sebastienbarre]

See Avoid old CSS flexbox (Google Lighthouse) · Issue #9 · tachyons-css/tachyons-flexbox.

I would suggest either passing the flexbox: 'no-2009' option to autoprefixer in tachyons-css/tachyons-build-css.

Or maybe use luisrudge/postcss-flexbugs-fixes: PostCSS plugin that tries to fix all of flexbug's issues, since the build pipeline is already based on PostCSS (see philipwalton/flexbugs: A community-curated list of flexbox issues and cross-browser workarounds for them.).