feat: added loop-black to colors.scss

Author: Hammerbak

web/profiles/custom/os2loop/themes/os2loop_theme/assets/signifly-variables/colors.scss

@@ -32,3 +32,6 @@ $loop-red: #dc3545;
 
 // System white
 $loop-white: #fff;
+
+// System black
+$loop-black: #000;