Manually add back foreground mixin

This seems to have been removed when foundation went to  6.3, and
wasn’t added back.

For:  #84

css/ebi-global-includes/_ebi_foundation_overides.scss

@@ -7,3 +7,27 @@
     -webkit-appearance: none;
   }
 }
+
+// manually add back the foreground mixin
+// https://github.com/ebiwd/EBI-Framework/issues/84
+// @import 'libraries/foundation-6/scss/util/util/math';
+
+/// Checks the lightness of `$color`, and if it passes the `$threshold` of lightness, it returns the `$yes` color. Otherwise, it returns the `$no` color. Use this function to dynamically output a foreground color based on a given background color.
+///
+/// @param {Color} $color - Color to check the lightness of.
+/// @param {Color} $yes [$black] - Color to return if `$color` is light.
+/// @param {Color} $no [$white] - Color to return if `$color` is dark.
+/// @param {Percentage} $threshold [60%] - Threshold of lightness to check against.
+///
+/// @returns {Color} The $yes color or $no color.
+@function foreground($color, $yes: $black, $no: $white, $threshold: 60%) {
+  @if $color == transparent {
+    $color: $body-background;
+  }
+  @if (lightness($color) > $threshold) {
+    @return $yes;
+  }
+  @else {
+    @return $no;
+  }
+}