more form style consistency improvements

sass/button.scss

@@ -90,3 +90,8 @@
     color: var(--color-link-hover);
   }
 }
+
+.button--danger {
+  @extend .button--link;
+  color: var(--color-error);
+}

sass/form.scss

@@ -64,11 +64,14 @@ fieldset-group {
 }
 
 fieldset-section,
+fieldset-group,
 form,
 .checkbox,
 .radio,
-.form-field--SimpleMDE {
+.form-field--SimpleMDE,
+.form-field__help {
   + fieldset-section,
+  + fieldset-group,
   + form,
   + .checkbox,
   + .radio,
@@ -76,6 +79,10 @@ form,
     margin-top: var(--spacing-l);
   }
 
+  + .form-field__help {
+    margin-top: var(--spacing-s);
+  }
+
   &:last-child {
     margin-bottom: 0;
   }