this version will run with npm start, but when attempting to run the built version behind nginx, it appears to have issues
PostCSS Flexbugs Fixes 
PostCSS plugin This project tries to fix all of flexbug's issues.
bug 4
Input
.foo { flex: 1; }
.bar { flex: 1 1; }
.foz { flex: 1 1 0; }
.baz { flex: 1 1 0px; }
Output
.foo { flex: 1 1; }
.bar { flex: 1 1; }
.foz { flex: 1 1; }
.baz { flex: 1 1; }
bug 6
Input
.foo { flex: 1; }
Output
.foo { flex: 1 1 0%; }
This only fixes css classes that have the
flexproperty set. To fix elements that are contained inside a flexbox container, use this global rule:
* {
flex-shrink: 1;
}
bug 8.1.a
Input
.foo { flex: 1 0 calc(1vw - 1px); }
Output
.foo {
flex-grow: 1;
flex-shrink: 0;
flex-basis: calc(1vw - 1px);
}
Usage
postcss([require('postcss-flexbugs-fixes')]);
You can also disable bugs individually, possible keys bug4, bug6 and bug8a.
var plugin = require('postcss-flexbugs-fixes');
postcss([plugin({ bug6: false })]);
See PostCSS docs for examples for your environment.