Move the conditional statement back to the file because nested imports aren't supported in Sass

scss/_utilities.scss

@@ -6,7 +6,4 @@
 @import "utilities/spacing";
 @import "utilities/text";
 @import "utilities/visibility";
-
-@if $enable-flex and $enable-grid-classes {
 @import "utilities/flex";
-}

scss/utilities/_flex.scss

@@ -2,6 +2,7 @@
 //
 // Custom styles for additional flex alignment options.
 
+@if $enable-flex and $enable-grid-classes {
   @each $breakpoint in map-keys($grid-breakpoints) {
     // Flex column reordering
     @include media-breakpoint-up($breakpoint) {
@@ -23,3 +24,4 @@
       .flex-#{$breakpoint}-bottom { align-self: flex-end; }
     }
   }
+}