add mixins to separately change main and heading colors for light/dark backgrounds

Author: yann-soubeyrand

css/theme/template/mixins.scss

@@ -36,10 +36,38 @@
 	}
 }
 
+@mixin light-bg-main-color( $color ) {
+	section.has-light-background {
+		color: $color;
+	}
+}
+
+@mixin light-bg-heading-color( $color ) {
+	section.has-light-background {
+		h1, h2, h3, h4, h5, h6 {
+			color: $color;
+		}
+	}
+}
+
 @mixin dark-bg-text-color( $color ) {
 	section.has-dark-background {
 		&, h1, h2, h3, h4, h5, h6 {
 			color: $color;
 		}
 	}
-}
+}
+
+@mixin dark-bg-main-color( $color ) {
+	section.has-dark-background {
+		color: $color;
+	}
+}
+
+@mixin dark-bg-heading-color( $color ) {
+	section.has-dark-background {
+		h1, h2, h3, h4, h5, h6 {
+			color: $color;
+		}
+	}
+}