Proposal

Author: louismaximepiton

scss/_maps.scss

@@ -149,6 +149,7 @@ $utilities-bg-subtle: (
 $utilities-border: map-merge(
   $utilities-colors,
   (
+    "black": to-rgb($black),
     "white": to-rgb($white)
   )
 ) !default;

site/content/docs/5.3/utilities/borders.md

@@ -49,6 +49,7 @@ Change the border color using utilities built on our theme colors.
 <span class="border border-{{ .name }}-subtle"></span>
 {{- end -}}
 {{< /border.inline >}}
+<span class="border border-black"></span>
 <span class="border border-white"></span>
 {{< /example >}}