Correctly expose and use variables so that they can be overridden

Author: tobiasahlin

src/marketing/support/variables.scss

@@ -7,7 +7,7 @@ $mktg-header-spacing-large: -0.03em !default;
 $mktg-header-spacing-default: -0.01em !default;
 $mktg-header-spacing-threshold: 48px !default;
 $mktg-header-weight-large: 800 !default;
-$mktg-header-weight-default: 600 !default;
+$mktg-header-weight-default: $font-weight-bold !default;
 $mktg-header-weight-threshold: 24px !default;
 
 // Header size steps

src/marketing/type/typography.scss

@@ -8,8 +8,8 @@
 .h6-mktg {
   font-family: $font-mktg;
   font-feature-settings: $mktg-font-feature-settings;
-  font-weight: $font-weight-bold !important;
-  letter-spacing: $mktg-header-spacing-default;
+  font-weight: $mktg-header-weight-default !important;
+  letter-spacing: $mktg-header-spacing-default !important;
 }
 
 @each $header, $sizes in $mktg-headers {