Make the comment syntax consistent across all CSS (#707)

* Update _article.scss

* Update _dark_variables.scss

* Update _forms.scss

* Update _global.scss

* Update _header.scss

* Update _variables.scss

assets/themes/default/_variables.scss

@@ -1,4 +1,4 @@
-// Color Scheme
+/* Color Scheme */
 $gray: #F3F3F3;
 $black: #242424;
 $white: #F8F8F8;
@@ -16,13 +16,13 @@ $primary: $purple;
 $primary-text-color: $white; // text color on primary background (buttons for instance)
 $success-color: $green;
 
-// Dimensions
+/* Dimensions */
 
 $article-width: 70ch;
 $horizontal-margin: 20%;
 $margin: 0 $horizontal-margin;
 
-// Fonts
+/* Fonts */
 
 $route159: "Route159", serif;
 $playfair: "Playfair Display", serif;