added usage

Author: gihanrangana

snippets/scss/layouts/dark-theme.md

@@ -1,6 +1,6 @@
 ---
 title: Dark Theme
-description: SCSS mixin to change styles for dark themes
+description: SCSS mixin to change styles for dark themes.
 tags: scss, css, mixin, snippet, dark-theme, layout
 author: gihanrangana
 ---
@@ -21,4 +21,12 @@ author: gihanrangana
 		}
 	}
 }
+
+// Usage:
+.container{
+	background: #f0f0f0;
+	@include isDark {
+		background: #222;
+	}
+}
 ```