chore: prepare for dark theme

src/scss/_colors.css

@@ -29,6 +29,10 @@
      @return $luminance
  }
 
+ @function getFontColor() {
+   @return getTextColorFromBackground(get-color("background-alt"));
+ }
+
  @function getTextColorFromBackground($background-color) {
      @if (luminance($background-color) < 255 * $whiteness_value) {
          @return $color-font-light;

src/scss/_typography.scss

@@ -21,7 +21,7 @@ body {
 	text-align: left;
   font-size:  $fontsize;
 	line-height: $lineheight;
-	color: $color-font;
+	color: getFontColor();
   font-weight: $fontweight_base;
 }