feat: add CSS Vars to border utilities

Author: mrholek

scss/_utilities.scss

@@ -88,42 +88,42 @@ $utilities: map-merge(
     "border": (
       property: border,
       values: (
-        null: $border-width solid $border-color,
+        null: $border-width solid $var(--#{$variable-prefix}border-color, $border-color),
         0: 0,
       )
     ),
     "border-top": (
       property: border-top,
       values: (
-        null: $border-width solid $border-color,
+        null: $border-width solid $var(--#{$variable-prefix}border-color, $border-color),
         0: 0,
       )
     ),
     "border-end": (
       property: border-right,
       class: border-end,
       values: (
-        null: $border-width solid $border-color,
+        null: $border-width solid $var(--#{$variable-prefix}border-color, $border-color),
         0: 0,
       )
     ),
     "border-bottom": (
       property: border-bottom,
       values: (
-        null: $border-width solid $border-color,
+        null: $border-width solid $var(--#{$variable-prefix}border-color, $border-color),
         0: 0,
       )
     ),
     "border-start": (
       property: border-left,
       class: border-start,
       values: (
-        null: $border-width solid $border-color,
+        null: $border-width solid $var(--#{$variable-prefix}border-color, $border-color),
         0: 0,
       )
     ),
-    "border-color": (
-      property: border-color,
+    "var(--#{$variable-prefix}border-color, $border-color)": (
+      property: var(--#{$variable-prefix}border-color, $border-color),
       class: border,
       values: map-merge($theme-colors, ("white": $white))
     ),