fix

scss/_button-group.scss

@@ -39,7 +39,7 @@
   // Prevent double borders when buttons are next to each other
   > :not(.btn-check:first-child) + .btn,
   > .btn-group:not(:first-child) {
-    margin-left: -$btn-border-width;
+    margin-left: calc($btn-border-width * -1); // stylelint-disable-line function-disallowed-list
   }
 
   // Reset rounded corners
@@ -126,7 +126,7 @@
 
   > .btn:not(:first-child),
   > .btn-group:not(:first-child) {
-    margin-top: -$btn-border-width;
+    margin-top: calc($btn-border-width * -1); // stylelint-disable-line function-disallowed-list
   }
 
   // Reset rounded corners

scss/forms/_input-group.scss

@@ -121,7 +121,7 @@
   }
 
   > :not(:first-child):not(.dropdown-menu)#{$validation-messages} {
-    margin-left: -$input-border-width;
+    margin-left: calc($input-border-width * -1); // stylelint-disable-line function-disallowed-list
     @include border-start-radius(0);
   }