PostCSS plugin for inserting a display:inline-block setting for IE9 every time display flex is used..
.foo {
display: flex;
}
.foo {
display: flex;
}
.ie9 .foo {
display: inline-block;
}
postcss([ require('postcss-ie9-flex-to-display-inline-block') ])
See PostCSS docs for examples for your environment.